Chapter 004, The Propeller Environment

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Select a sample pump capable of lifting a sample a vertical distance of 6. On reaching a preselected pressure, a pneu- matic relay E releases the accumulated propellant through inlet line F to the sample intake chamber G. Pressure in the chamber closes its chor. Excess propellant vents through the sample line, thereby purging it of liquid and incidentally providing protection against line freezing in cold weather. The resulting pressure drop recloses the relay E and the sampling cycle repeats at a repeti- tion rate determined by adjusting the control valve B.

Scoop Counter Weight not shown 7. Alum, Sampler Support If a program requires maintaining isokinetic conditions, dial adjustment of intake velocity is a desired feature. The desired features of sample storage subsystems are: Flexibility of discrete sample collection with provision for single composite container. Minimum discrete sample container volume of ml 0. Storage capacity of at least 24 discrete samples.

Containers of conventional polyethylene or borosilicate glass and of wide mouth construction. Adequate insulation for the sampler to be used in either warm or freezing ambient conditions. Battery life for two to three days of reliable hourly sampling without recharging. Battery weight of less than 9 kg 20 Ib. Solid state logic and printed circuit boards.

Timing and control systems contained in a waterproof compartment and protected from humidity. Timer should use solid state logic and a crystal controlled oscillator. Controls directly linked to a flow meter to allow both flow-proportional sampling and periodic sampling at an adjustable interval from 10 minutes to 4 hours. Capability of multiplexing, that is, drawing more than one sample into a discrete sample bottle to allow a small composite over a short interval. Also capability for filling more than one bottle with the same aliquot for addition of different preservatives.

Capability of adjusting sample size and ease in doing so. Water tight casing to withstand total immersion and high humidity. Vandal proof casing with provisions for locking. A secure harness or mounting device if sampler is placed in a sewer. Sized to fit in a standard manhole without disassembly.

Compact and portable for one-man installation. Overall construction, including casing, of materials resistant to corrosion plastics, fiberglass, stainless steel. Exterior surface painted a light color to reflect sunlight. Low cost, availability of spare parts, warranty, ease of maintenance, reliability and ruggedness of construction. A few general guidelines follow: When a sampler is installed in a manhole, secure it either in the manhole, for instance, to a rung above the high water line or outside the manhole to an above ground stake by means of a rope.

Place the intake tubing vertically or at such a slope to ensure gravity drainage of the tubing between samples, avoiding loops or dips in the line. Clean sample bottles, tubing and any portion of the sampler which contacts the sample between setups. Whatever methods of cleaning are used, all parts of the sampler which come in contact with the sample should be rinsed with tap water and then given a final rinse with distilled water. A distilled water rinse may not be necessary between setups on the same waste stream.

Inspect the intake after each setup and clean, if necessary. Exercise care when placing the intake s in a stream containing suspended solids and run the first part of the sample to waste. Maintain sufficient velocity of flow at all times to prevent deposition of solids. When a single intake is to be used in a channel, place it at six-tenths depth point of average velocity. Maintain electrical and mechanical parts according to the manufacturer's instructions. Replace the desiccant as needed.

Position the intake in the stream facing upstream. Limit the orientation of the intake 20 degrees on either side of the head-on. Secure the intake by a rope at all times with no drag placed on the inlet tubing. After the installation is complete, collect a trial sample to assure proper operation and sample collection. The sampler must give replicate samples of equal volume throughout the flow range. If the sampler imposes a reduced pressure on a waste stream containing suspended solids, run the first part of the sample to waste.

Place the sampler below the freezing level or in an insulated box. When AC is available, use a light bulb or heating tape to warm sampler. When installation below the freezing level is not possible and line current is available wrap 1. Loosely wrap a large 10 mL plastic trash bag over the heat tape on the intake lines.

Place a large plastic bag over the sampler as loosely as possible. Even with a back-purge system, some liquid will remain in the line unless gravity drainage is provided. If an excess length of tubing exists, cut it off. Keep all lines as short as possible. Do not use catalytic burners to prevent freezing since vapors can affect sample composition. When power is unavailable, use a well insulated box containing the sampler, a battery and small light bulb to prevent freezing. The following is a list of features to be considered in selecting an automatic sampler: Oils and grease and floating material 8, Materials - Organic pollutants 9.

Ease of operation It can be taken manually, using a pump, scoop, vacuum, or other suitable device. The collection of a grab sample is appropriate when it is desired to: Characterize water quality at a particular time. Provide information about minimum and maximum concentrations. Allow collection of variable sample volume. Meet a requirement of a discharge permit. The number of discrete samples which make up the composite depends upon the variability of pollutant concentration and flow.

A sequential composite is defined as a series of periodic grab samples each of which is held in an individual container, then composited to cover a longer time period. Six methods are used for compositing samples. Choice of composite type is dependent on the program and relative advantages and disadvantages of each composite type. The stream does not flow continuously such as batch dumps. The water or waste characteristics are relatively constant. Information on maximum, minimum or variability is desired.

The history of water quality is to be established based on relatively short time intervals.

Handbook for Sampling and Sample Preservation of Water and Wastewater

Use composite samples when: The preparation of the flow rated composite is performed in various ways, Table 2. A ml discrete sample was taken at the end of each hour over an eight hour shift. A 3, ml composite is desired. A recording of totalized flow is available. Check to see if maximum a. If it does, adjust aliquot sizes using the relationship: Determine the adjusted composite volume from a. This example illustrates that although desired composite volume was 3, ml V because of discrete sample volume size, only 2, ml w of composite sample can be obtained. A ml discrete sample was taken at the end of each hour over an 8 hour shift.

A recording of flow rate is available. A 2, ml composite is desired. Check to see if maximum a.. This example illustrates that with an individual discrete sample capacity of ml only 1, ml volume of composite sample can be obtained. If it is desired to collect a composite sample of 3, ml volume, obviously larger sized ml capacity bottles or greater sampling frequency will be required for collecting individual discrete samples.

A mL discrete sample was taken each time an average hourly flow flowed past the sample point. Sampling period is eight hours. In addition, a ml sample was taken at the end of the sampling period. A composite of 4, ml is desired. A recording of total flow from past record is available. Sample liters liters ml No. Determine the number of samples from the overall sampling period. On the basis of the number of samples required for the overall sampling period, P, determine the average flow from the past records for the time interval, T, between the successive discrete samples.

Collect each discrete sample every time 3, L passes the sampling point; and an additional one ml sample aliquot at the end of the sampling period. Record the actual flow. Note the total flow for the sampling period. In our case it is EAQ,. Calculate the difference between ZAQ. This is the flow which passes the sampling point after taking the last sample for equal incremental discharge, up to the end of sampling. This flow is sampled by the sample taken at the end of the sampling period. Compute the representative aliquot required for the unbalanced flow in step 7 in proportion to the equal increment flow.

Given; A ml discrete sample was taken each time an average hourly flow flowed past the sample point. In addition, a ml sample was taken at the end of the sampling period, A composite of 4, ml is desired. A recording of instantaneous flow rate from past records is available. On the overall sampling the past records for the screte samples. Collect a discrete sample each time liters passes the sampling point and one additional aliquot of ml at the end of the sampling period. Record the actual flows per unit of time interval selected. For example; hours, minutes, days.

Calculate the total actual flow for the the sampling period. In our case it is EAQ. This is the flow which passes the sampling point after taking the last sample for equal incremental discharge, up to the end of the sampling period. Compute the representative aliquot required for the unbalanced flow determined in step 7 in proportion to the equal increments. The planning process can be divided into four stages: This information may be available from records of previous surveys. Where such information is not available, carry out a reconnaissance survey to become thoroughly familiar with actual site conditions.

Collect the appropriate information for Table 2. Delineate preliminary sampling objectives and details of the plan such as anticipated parameters, sample type, sample size, and frequency, specified. Record this information in a tabular form similar to Table 2. Make an estimate of the resources manpower and equipment needed for the sampling program. Include into the preliminary sampling plan, sample preservation and chain of custody procedures.

Process Details Industry 2. Automatics Samplers Type Manual Samplers: Wading rods Cable lines Sounding rods Sounding Weight: Spell out the final plan in detail including: Pre-sampling briefing should be a key element in any sampling program. The performance evaluation should enhance the efficiency of the program and quality of the data generated from a sampling program. If proper precautions and care are not exercised in the field procedures, the entire sampling program will become meaningless despite adequate planning, analytical facilities, and personnel.

The key to the success of a field sampling program lies in good housekeeping, collection of representative samples, proper handling and preservation of samples, and appropriate chain of custody procedures. Compose written instructions on field sampling procedures. Prior to use, check sampling equipment to insure good operating conditions and cleanliness. Keep the equipment ready to be used. After the sampling has been completed, clean the equipment and keep it in neat environments. Follow manufacturer's specifications in carrying out routine maintenance of the equipment.

At the appropriate place as defined in sampling program. Upstream and downstream conditions meet the requirement of specific installation of primary and secondary devices. Dimensions of primary devices such as flumes, weirs, and still wells to be sure they are within tolerance limits. General conditions of channel, primary and secondary devices and stilling wells. Note any unusual wear, debris in channel or distortion of chart paper. Calibration of primary and secondary devices before actual measurements of flow are taken. Check all sample bottles to avoid contamination. Clean the bottles as indicated in Section If this cannot be done, do not collect the sample.

In the laboratory, clean the sample intake tubing by flushing with hot water and then rinsing with distilled water. In the field, rinse several times with sample water. Maintain record of breakdowns in the sampling operations, the problems encountered with different equipment and how they were resolved. This information indicates the reliability of the equipment, the problem areas that need to be brought to the manufacturer's attention, and considerations for future procure- ments.

Hold training sessions for field sampling teams. Collect the sample where water is well mixed, that is near a Parshall flume or at a point of hydraulic turbulence such as downstream of a hydraulic jump. Certain types of weirs and flumes tend to enhance the settling of solids upstream and accumulate floating solids and oil downstream, therefore such locations should be avoided as a sample source. For low level turbulence, mechanical or air mixing should be used to induce turbulence except when dissolved gases or volatile materials are being sampled.

Collect the sample in the center of the channel at 0. This depth avoids bottom bed loads and top floating materials such as oils and grease. In a wide channel, divide the channel cross section into different vertical sections so that 'each section is equal width. Take a representative sample in each vertical section. In a deep stream or lake, collect the samples at different depths. In those cases of. When manual sampling with jars, place the mouth of the collecting container below the water surface and facing flow to avoid an excess of floating material.

Keep the hand away from the mouth of the jar as far as possible. Additional guidelines for manual sampling: Sample facing upstream to avoid contamination. Force sampling vessel through the entire cross section of the stream wherever possible. Drop an inverted bucket and jerk line just before impact with the water surface.

Be certain that the sampler closes and opens at the proper time when sampling with a depth integrating sampler; with a point sampler, be certain that sampler opens at a proper depth. If a doubt exists, discard the sample and re-sample. When sampling, it is necessary to fill the bottles completely if the samples are to be analyzed for volatile organics, CL, CO-, NH.

FE , oil and grease, acidity or alkalinity. When sampling for bacteria or suspended solids, it is necessary to leave an airspace in the sample container to allow mixing before subsampling. Collect sufficient volume to allow duplicate analyses and quality assurance testing split or spiked samples. The required sample volume is a summation of that required for each parameter of interest. Maintain an up-to-date log book which notes possible interferences, environmental conditions and problem areas. Since mathematical relationship between volumetric flow and height or depth of flow is nonlinear, composite flow proportional samples in relation to the total volume of flow as opposed to gauge height or raw measurement of a secondary device.

If samples are taken from a closed conduit via a valve or faucet arrangement, allow sufficient flushing time to insure that the sample is representative of the supply, taking into account the diameter, length of the pipe to be flushed and the velocity of the flow. Follow these guidelines for sample handling and preservation: Minimize the number of people handling the sample. Follow the guidelines given in chapters 15 and 17 on chain of custody procedures and sample handling. Store the sample in a manner which insures that the parameters to be analyzed are not altered, and use the preservation methods and holding times pertinent to the parameters shown in chapter Insure that the container material does not interfere with the analysis of the specific parameters.

Field laboratories must also have standard procedures and methods for handling and analyzing samples such that identification, integrity and representativeness of the samples are maintained at all times. Water Monitoring Task Force. Procedures for Sampling and Measuring Industrial Wastes. Sewage and Industrial Wastes, 24, pp. Environmental Protection agency, Cincinnati, Ohio. An assessment of Automatic Sewer Flow Sample.

Prepared for the Office of Research and Monitoring, U. Environmental Protection Agency, Washington, D. Contamination by Oceanographic Samplers. National Field Investigation Center, Denver. Metcalf and Eddy Inc. Government Printing Office, Washington, D. Comparison of Wastewater Sampling Techniques J. Handbook for Industrial Wastewater Monitoring.

Geological Survey, as well as texts or manuals on hydraulics. Therefore, care must be exercised in selecting a flow measurement site. The ideal site gives desired flow measurement to meet program objectives, provides ease of operation and accessibility; personnel and equipment safety, and freedom from vandalism. A flow measurement system usually consists of a primary device having some type of interaction with the fluid and a secondary device which translates this interaction into a desired readout or recording. Closed conduit flow measurement 2.

Flow measurement for pipes discharging to atmosphere 3. Open channel flow measurement 4. Miscellaneous methods of flow measurement Table 3. Basically the Venturi meter is a pipe segment consisting of an inlet section a converging section , a throat and an outlet section a diverging section as illustrated in Figure 3. One of the advantages of the Venturi meter is that it has low pressure loss. Manufacturers of Venturi meters routinely size their meters for a specific use.

The accuracy of the Venturi meter is affected by changes in density, temperature, pressure, viscosity and pulsating flow of the fluid. To obtain accurate flow measurements: Install Venturi meter as per manufacturer's instructions. Install Venturi meter downstream from a straight and uniform section of pipe, at least diameters, depending upon the ratio of pipe diameter to throat diameter and whether straightening vanes are installed upstream.

Installation of straightening vanes upstream will reduce the upstream piping. For wastewater application, insure that the pressure measuring taps are not plugged. Calibrate Venturi meter in place either by volumetric method Section 3. C varies with Reynold's number, meter surfaces and installation. The Dall tube is a Venturi type device, in which the differential pressure results from the streamlined bending as well as the velocity head Figure 3.

The Dall tube is almost as accurate and has a higher head recovery than the standard Venturi, being one of the lowest permanent head loss devices known. It is more sensitive to system disturbances than the Venturi, and straight upstream pipe runs of 40 pipe diameters or more may be required. Installation of straightening vanes upstream will reduce the upstream piping requirement. Although somewhat cheaper than the Venturi, the Dal! It'is much shorter than either long or short tube Venturi meters. Calibration and other installation guidelines for Venturi meters also apply to flow tubes.

It operates on the same principles as the Venturi meter. The flow formula for the Venturi tube is also applicable to the nozzle. Flow nozzles can be used in wastewater flows containing moderate amounts of suspended solids. Each manufacturer uses a slightly different nozzle ranging from a Venturi to an orifice. Accuracy, installation and calibration guidelines for Venturi meters also apply to flow nozzles.

Basically, an orifice is an obstacle placed in the path of flow in a pipe. The principles of operation of an orifice are the same as for nozzles and Venturi meters since the stream lines of the flow and the basic formula are similar to those of a Venturi meter. The nominal coefficients are applicable for relatively large orifices operating under comparatively large heads of water.

The orifice measures flow over a wide range by varying the throat width. Orifice Diameter d2 0. It is not uncommon to need 40 to 60 pipe diameters of straight run upstream of the installation. The other disadvantage of the orifice is susceptibility to clogging in waters with high suspended solids concentration. The pressure on the outside of an elbow is greater than on the inside, and the pressure taps located midway around the bend at about 45 degrees from either flange can be connected to a suitable secondary element for indicating or recording.

For accurate flow measurement, straight pipe runs of at least 20 pipe diameters should be provided both upstream and downstream of the elbow. In operation, the velocity of the flow is calculated from the difference in head measured on the manometer. Pitot tubes measure the flow velocity at a point.

The basic formula is: Pitot tube measurements should be made in a straight section upstream and free of valves, tees, elbows, and other fittings with a minimum distance of 15 to 50 times the pipe diameter. When a straight section is not possible, a velocity profile should be obtained experimentally to determine the point of mean velocity.

Pitot tubes are not practical for use with liquids with large amounts of suspended solids because of the possibility of plugging. In large pipes, the Pitot tube is one of the most economical means of measuring flows, except for low velocities. A metal float in the tube comes to equilibrium at a point where the annular flow area is such that the velocity increase has produced the necessary pressure difference. Rotameters are simple, inexpensive and accurate devices for measuring relatively small rates of flow of clear, clean liquids no suspended solids.

For this reason they are used to measure the water rate into individual processing steps in manufacturing operations. To maintain accuracy in a rotameter, it is essential that both the tube and float be kept clean. In the electromagnetic flowmeter, the conductor is the liquid stream to be measured and the field is produced by a set of electromagnetic coils. A typical electromagnetic flowmeter is shown in Figure 3. The induced voltage is subsequently transmitted to a converter for signal conditioning. Electromagnetic flowmeters are used in full pipes and have many advantages: However, they are expensive and build-up of grease deposits or pitting by abrasive wastewaters can cause error.

Regular checking and cleaning of the electrodes are necessary. Flowmeters must be installed according to manufacturer's instructions and calibrated in place to eliminate errors due to uncertainties in non-laminar flow profile, and due to acoustic short circuit where transducers are mounted externally on the pipe. According to the manufacturers, an accuracy of one percent of full scale is achievable.

The orifice and flow nozzle techniques which are not listed here are described in Sections 3,1. Rotating element meters are described in Section 3. Vertical open end pipe 7 a.

Intermediate Shafting

California Pipe Method Figure 3. To obtain the flow, the trajectory measurements X and Y, Figure 3. Horizontal or sloped open end 7 Q- 2. Purdue Method 6 This method can be used for partially full pipe discharging to atmosphere using the curves Figure 3. Different methods in use can be grouped into the following broad classification: Various drag body current meters are compared in Table 3.

The principle of operation is based on the proportionality between the velocity of water and resulting angular velocity of the meter rotor. In conventional current meters there is a wheel which rotates when immersed in flowing water and a device which determines the number of revolutions of the wheel. The general relation between the velocity of the water and number of revolutions of the wheel is given by: Practical considerations limit the ratings of these meters to velocities of 0.

The comparative characteristics of these two types are summarized below: Vertical -axis rotor with cups or vanes a. Operates in lower velocities than do horizontal-axis meters. Bearings are well protected from silty water. Rotor is repairable in the field without adversely affecting the rating. Single rotor serves for the entire range of velocities. Horizontal-axis rotor with vanes a. Rotor disturbs flow less than do vertical-axis rotors because of axial symmetry with flow direction.

Rotor is less likely to be entangled by debris than are vertical-axis rotors. Bearings friction is less than for vertical-axis rotors because bending moments on the rotor are eliminated. Vertical currents will not be indicated as positive velocities as they are with vertical-axis meters. They have a higher frequency of mechanical problems. To determine the discharge flow volume , in additions to velocity of flow it is necessary to determine the area of flowing water or wastewaters. This holds especially for large flows in rivers, lakes, and wide and deep channels. A depth sounding is necessary at each vertical and width measurement of the cross-section of flow to determine the area of flowing water or wastewater.

Sounding rods, sound weights and reels, handlines, and sonic sounders are common equipment used for depth determinations. Marked cableways and bridges, steel or metallic taps or tag lines are used for width determinations. For details or procedures for depth and width determinations, see reference. In drag body current meters such as vertical-axis deflection vane, horizontal-axis pendulum type deflection vane and pendulum current meters, it is possible to integrate velocities at different depths in a particular section to obtain the mean velocity of flow, whereas inclinometer, drag sphere, rotating element current meters and pitot tubes measure velocity at a point.

Therefore, to obtain the mean velocity of flow at a particular vertical section, it is necessary to take velocity measurements at different depths. The various methods of obtaining mean velocities are: Salt Velocity Method 1 2 5 6 The method Is based on the principle that salt in solution increases the conductivity of water. Sodium chloride and lithium chloride are commonly used.

The basic procedure Is as follows: Install two pairs of conductivity electrodes down stream from the salt injection point at known distances and sufficiently far apart in the stretch of the channel. Connect the recording galvanometer to the electrodes. Inject the slug of salt solution. The time for salt solution to pass from the upstream to the down- stream electrodes, in seconds, is determined by the distance on the graph between the centers of the gravity of the peak areas.

Color Velocity Method The color velocity method is used to estimate high velocity flows in open channels. It consists of determining the velocity of a slug of dye between two stations in the channel. This velocity, taken as the mean velocity, multiplied by the cross-sectional area of flow gives an estimate of the discharge. Commercially stable dyes see section 3.

The color velocity is computed from the observations of the time of travel of the center of the mass of colored liquid from the instant the slug of dye is poured at the upstream station to the instant it passes the downstream station, which is at a known distance from the upstream station.

With fluorescent dyes, the use of a fluorometer to detect the center of the colored mass will enhance the accuracy of the results. There are three types of float methods used for estimating flow measurements; surface floats, subsurface floats and integrating floats. To determine the flow velocity, one or more floats are placed in the stream and their time to travel a measured distance is determined. These methods are simple, but from an accuracy standpoint, they should only be used for estimating the discharge.

Various surface floats such as corks and stoppered bottles and submerged floats like oranges, measure the surface velocity. The mean velocity of flow is obtained by multiplying with a coefficient which varies from ff. These rods have a weighted end so that they float in vertical position with the immersed length extending about nine-tenth of the flow depth.

Velocity measured by the time of travel by these rods is taken as the mean velocity of flow. These floats are used in open channels and sewers. To obtain better results, the velocity measurements should be made on a calm day when in a sufficiently long and straight stretch of channel or sewer of uniform cross-section and grade with a minimum of surface waves.

Choose a float which will submerge at least one-fourth the flow depth. A more accurate velocity measurement is obtained by using integrating float measurements. The method is simple and consists of the release of buoyant spheres resembling like ping pong balls from the channel floor. As these spheres rise, they are carried downstream by the flow velocity.

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The time from the moment of release to the moment when they surface, and the distance traveled downstream are measured and inserted into the following equations to determine the flow rate. In flows of large depth and velocity, integrating float methods with two floats of different velocities of rise are used. The integrating float method is simple and does not require any laboratory calibration. It integrates the vertical velocity profile and yields the mean velocity or discharge per unit width of the section. The method is suited to low velocities and is especially useful for flows having abnormal velocity profiles, and it has practically no lower velocity limit.

To get better accuracy, the reach of the stream to be measured should be sufficiently long and straight and the bed fairly uniform. Use a fast rising float so that distance travelled downstream is of short length. The shape of the float should be spherical. Depending upon the shape of the opening, weirs may be termed rectangular, trapezoidal, or triangular. When the water level in the downstream channel is sufficiently below the crest to allow free access of air to the area beneath the nappe, the flow is said to be free.

When the water level under the nappe rises above the crest elevation the flow may be considered submerged: Therefore, the use of submerged weirs as the flow measuring device is avoided. In a sharp crested weir, flowing liquid does not contact the bulk head but springs past it. If the bulk head is too thick for the liquid to spring past, the weir is classed as broad crested. Weirs may be contracted or suppressed.

When the distances from the sides of the weir notch to the sides of the channel weir pool are great enough at least two or three times the head on the crest to allow the liquid a free, unconstrained lateral approach to the crest, the liquid will flow uniformly and relatively slowly toward the weir sides. As the flow nears the notch it accelerates, and as it turns to pass through the opening, it springs free laterally with a a contraction that results in a jet narrower than the weir opening. If a rectangular weir is placed in a channel whose sides also act as the sides of the weir, there is no lateral contraction, and the weir is called a suppressed weir.

Various types of weirs are shown in Figure 3. Most of the flow measurements are conducted on sharp crested weirs without submergence and the subsequent discussion is limited to this type. For information on sharp crested weirs with submergence and broad crested weirs, refer to reference 2 and other books on hydraulics. A typical sharp crested weir is shown in Figure 3.

The relationship between head and discharge for different weirs is given in Table 3. For rectangular weirs, the Francis formula is widely used for flow measurements. However, it should be born in mind that it is applicable and accurate only for sharp crested fully contracted or suppressed weirs. Contracted Cipolletti Weir Figure 3. It gives accurate results and is being increasingly used. The rate of flow determines the type of weir to use.

A rectangular weir is preferable for flows greater than 3. V-notch weirs are used for flows of less than 0. The accuracy of measurements obtained by the use of Cipolletti weirs, based on the formulas given in Table 3. The crest should be placed high enough so that the water flowing over will fall freely, leaving an air space under and around the jets. Requirements for standard weir installations are shown in Figures 3.

For shapes other than those mentioned above, head-discharge relationship must be established through field calibration using the salt-dilution Section 3. Flow rates for Cipolletti weirs can be obtained from Figure 3. The upstream face of the bulkhead should be smooth and in a vertical plane perpendicular to the axis of the channel. The upstream face of the weir plate should be smooth, straight, and flush with the upstream face of the bulkhead. The entire crest should be a level, plane surface which forms a sharp, right-angled edge where it intersects the upstream face.

Both side edges of rectangular weirs should be truly vertical and of the same thickness as the crest. The upstream corners of the notch must be sharp. Based on Francis Weir formula as follows: Knife edges should be avoided because they are difficult to maintain. The downstream edges of the notch should be relieved by chamfering if the plate is thicker than the prescribed crest width.

This chamfer should be at an angle of 45 or mo. The distance of the crest from the bottom of the approach channel weir pool should preferably be not less than twice the depth of the water above the crest and in no case less than 0. The distance from the sides of the weir to the sides of approach channel should preferably be no less than twice the depth of water above the crest and never less than 0,31 m 1 foot. The overflow sheet nappe should touch only the upstream edges of the crest and sides. Air should circulate freely both under and on the sides of the nappe, The measurement of head on the weir should be taken as the difference in elevation between the crest and the water surface at a point upstream from the weir a distance of four times the maximum head on the crest.

The cross-sectional area of the approach channel should be at least 8 times that of the overflow sheet at the crest for a distance upstream from 15 to 20 times the depth of the sheet.

If the weir pool is smaller than defined by the above criteria, the velocity of approach may be too high and the staff gauge reading too low, and the head discharge relationship given in Section 3. Flumes are comprised of three sections: The flume size is given by the width of the throat section. Consider the following factors in the location of a flume: Do not install flume too close to turbulent flow, surging or unbalanced flow or poorly distributed velocity pattern. Locate flume in a straight channel section having no bends upstream of the flume.

For convenience install flume at a location which is readily accessible, near the diversion point, and near the devices installed to control the discharge.

Intermediate Shafting

Parshall Flumes Parshall flumes have been developed with throat width from 2. The configuration and standard nomenclature for Parshall flumes is given in Figure 3. Strict adherence to all dimensions is necessary to achieve accurate flow measurement. Flow through a Parshall flume may be either free or submerged. The flow is submerged if the submergence ratio is: Nomographs, curves or tables are readily available to determine the discharge from head observations.

Flow curves are shown in Figure 3. These correction factors are given in Figure 3. OOO , , , Standard Palmer Bowlus flumes are available to fit pipe sizes Diskin flumes, 24 an unconventional type of Palmer Bowlus flume, are portable devices but have limiting submergence, H. Cut-throat Flumes These are in a way modified Parshall flumes without throat section and flat bottom.

They are suitable for flat gradient channels; level flow and every flume size having the same wall lengths makes construction easy and less costly. Analytical and experimental background on these flumes can be found in reference Their main advantage is simplicity of construction, and they have a wide range of flow. Details on discharge ratings can be found in references 2 and Their design incorporates the sensitivity of a sharp crested weir and the self cleansing feature of a Parshall flume.

Other Flumes Trapezoidal flumes Figure 3. Two common types of flumes are: The San Dimas flume Figure 3. These flumes have the advantage that neither approach conditions nor disturbances upstream or downstream affect their discharge ratings. Their rectangular cross-section makes them less sensitive or accurate at low flows. The Manning formula is commonly used for estimating flow: The Manning formula is widely used for the engineering design of sewers and channels. However, for flow measurement, its usefulness is limited for a number of reasons.

It is difficult to assign an appropriate value to the roughness coefficient which varies with the channel or sewer material concrete or brick , and the surface of the channel or sewer new or old. For sewers, it varies also with the ratio of depth of flow to the depth when flowing full.

The other inaccuracy that may enter into the flow measurement is due to the slope of the energy grade line which is taken as the slope of the channel or sewer. However, these two slopes may or may not be identical. For various charts, tables and nomographs on the use of the Manning formula refer to reference These techniques require a license from Nuclear Regulatory Commission, are simple and relatively inexpensive, and the equipment is portable.

These techniques require a section of the pipe or channel free of branch connections and turbulence at the injection point for thorough mixing of the tracer. The tracer must be a gamma-ray emitter, must be compatible with the flowing liquid, and must have a half-life longer than the duration of the test. Tracers generally used are salts of cesium, iodine, sodium 24, "or gold There are two methods of flow measurements by the radioactive tracers: Two-Point Method This method uses the time interval for the surge of tracer to pass between two points separated by a determinable volume of the liquid.

This time interval is determined by peaks on the chronological chart of a common amplifier-recorder connected to two G-M counters separated by a known or determinable volume of a section of a pipe. The schematics of the the arrangement of the test is shown in Figure 3. Total- Count Method The basic principle of the total-count method is that a well mixed finite quantity of radiotracer, A, passing through a measurement point will produce a total number of N counts on a Sealer connected to a Geiger counter fixed in or near the stream some distance downstream.

The value of N is inversely proportional to the flow rate q and is directly proportional to A, the quantity of the tracer mixed: Note that q is the flow rate at the tracer injection point. The Total-Count Method gains versatility through the divided-stream principle: The same number of counts is obtained on the fraction or split flow as is obtained on the total flow. This allows one to measure a small fraction or bypass of the total flow.

To obtain accurate results, the numerical value of F must be determined in the laboratory by exposing the counter to a tracer solution in the same geometrical arrangement as in the field test, to find the counting rate that corresponds to a certain concentration of the tracer. Strap the Geiger counter to the and connect it to a sealer. Determine the number of counts per minute Then the factor, G, for cubic meters per minute gallons per min. To place the measurement, inject a known amount of tracer, A, either in a slug or gradually and record the total number of counts, N.

Calculate the flow using the formula: The divided-stream principle is used in sample-bucket technique, in which a fraction a bucket containing the counter. The factor bucket and the counter. The value of F, is predetermined by submerging the counter at least For better sensitivity a bundle of four counters connected in parallel and enclosed in lucite pipe is used. It does not require measurement of the stream dimensions or the measurements of fluid levels or pressures.

The flow is determined by measuring the concentration of the chemical at two points downstream from the injection point. The following should be considered when using this technique for flow measurements in waters and wastewaters: Turbulence at the point of injection of the chemical should assure thorough mixing especially the lateral mixing of the chemical in the field. Flow in the channel or pipe should be steady. Chemical used should meet the following requirements: Compatible with the fluid; no loss or deterioration of the chemical in the fluid.

Non-toxic to plant and animal life. Easy and accurate quantitative detection at low concentration. Low cost of the chemical and the equipment.

Chemicals commonly used are lithium chloride atomic adsorption analysis of lithium and fluorescent dyes fluorometer measurement such as sodium fluorescein, Rhodamine B, Pontacyl Brilliant Pink B, and Rhodamine WT. However, use of sodium fluorescein is not recommended as it is easily affected by light and bacterial action.

Conti nous-Addi ti on-of-Chemi cal-Method In this technique the chemical of known concentration is added at a uniform rate to the stream and the dilution is determined after it has traveled downstream far enough to assure complete mixing. Samples collected at various points across the cross-section which show the same dye concentration will verify complete mixing. Slug Injection Method In this method, a known amount, S, of the chemical is added to the stream at a point sufficiently downstream to assure complete mixing.

This technique is used in a confined area, such as the industrial plant. Water meters should be certified periodically. When using the incoming and outgoing flow for an initial estimate of the flow rate, all changes in the water quantity that occur in various processes must not be overlooked. To accomplish this, the. One method is to multiply the pumping time and the pump capacity at the discharge pressure as obtained from manufacturer's head curves versus flow.

However, these techniques should be used only for estimates of flows. The flow rate is then established for a specific time. More than one measurement is necessary to allow accurate estimates; the volume chosen should allow time for collection to be more than 10 seconds. These devices can be classified into two broad classes: Non-recording type with a. Direct read-out such as a staff gauge. Indirect read-out from fixed points as in a chain, wire weight and float type.

Recording type, where the recorders may be graphic or digital. Examples of recording type devices are: Bubbler tube Surface float Dipper Ultrasonic Common, accurate No compressed air source can be directly linked to sampler Self cleaning, less expensive; reliable Inexpensive, reliable Quite reliable, easy to operate No electrical or mechanical contact Manual only, stilling well may be needed Can clog openings, expensive Ne.

Propellers and Shafting for Sustainable Shipping

Care must be taken to install the gauges solidly to prevent errors caused by change in elevation of the supporting structure. The gauge hook is manually brought to the water surface and the water elevation read. Water level is indicated by raising or lowering the weight until it just touches the water surface. Sources of errors in the measurement are; settling of supporting structure, temperature changes, changes in length due to wear and wind action.

The reel is graduated or a counter is used to give readings from a reference check bar of the water elevations to the tenths and hundredths of a foot. The wheel is connected mechanically or electronically to the read-out or recorder.

The float is installed in a stilling well. This back pressure can be translated into water depth and subsequently related to discharge. The probe or sensor is part of an electrical circuit, and its behavior in a circuit is a function of its degree of immersion. Of the two physical arrangements, -liquid path and air path measurement, the air path arrangement is commonly used since installation is simplified, is independent of fluid velocity, and avoids any contact with the fluid.

In many instances, the discharge tables, charts or formulas have been developed empirically. They show experimental relationships. Therefore, extrapolation beyond the range of observations from which they were developed can lead to serious errors. An error of 0. A corresponding error in 0. Error due to transverse slope of weir crest. When the crest of the rectangular or Cippoletti weir is sloped, the common practice is to measure the head at the center of the crest.

This leads to an error of? Stilling well not at a proper location. The head of the weir must be measured beyond the effect of the drawdown. For standard weirs the stilling well for the head measurement should be placed at a distance upstream of four times the maximum head on the weir.

For Parshall flumes the locations of stilling wells for the head measurement bear a definite relationship with the throat width. Substantial errors in the field measurements have been traced to changes in the location or design of the stilling well entrance. Errors due to neglecting velocity of approach to weir. When the velocity of approach is greater than 0.

Propellers and Shafting for Sustainable Shipping

This error is less when the head on the weir is greater. Use of the Kindsvater-Carter formula will help alleviate this error. The error due to the reduction of depth of the weir pool. The height of the weir, when less than twice the head on the weir, will introduce an error of 5.

A corresponding error of a 0. This error can be corrected by using Rehbock's formula: Weir blade sloping upstream or downstream. The error introduced is normally small. It becomes significant, however, if the face goes out of plumb by a few degrees. Roughness of upstream face of weir or bulkhead. The roughness of the upstream face of weir or bulkhead can cause an increase in the discharge.

The discharge is observed to increase by changing the roughness of the upstream face of the wier bulkhead from that of a polished brass plate to that of a coarse file for a distance of Insufficient aeration of the nappe will increase the discharge over the weir. It has been observed that for a drop in pressure under the nappe by This error is of the same magnitude as the error for misreading the head.

Error due to misreading the head. Popular causes of this error are incorrect location of the gauge, a dirty head gauge, not using the stilling well, considerable fluctuations of the water surface and carelessness on the part of the reader. For greater heads, the error is less. The chart related errors are common to all the recording type devices. Intermediate shafts are used to transmit the power from the main engine to the tailshaft, and as such must be supported on bearings. These bearings are also referred to as plummer blocks, tunnel bearings or line shaft bearings.

The shafting may be supported on one or two bearings depending upon the design. The bearings are required to hold the shaft and support the shaft load as well as maintaining a satisfactory alignment. Plummer blocks are individual bearings which usually have their own oil supply contained within the bearing.

There are arrangements in which they can be supplied from an external source with their own oil supply and cooler system. Individual bearings, however, have a cooler contained within the plummer block, with cooling supplied from one of the sea water cooling systems. There are two types of bearing used in the intermediate shafting. The first type, most familiar to engineers, is that of the steel shaft rotating in a white metal bearing which is oil lubricated. This type of arrangement is used in high powered installations. The second type, similar to bearings used in pumps etc.

These bearings are split because of the difficulty in fitting them. The aim of the first type of bearing is to provide a good hydrodynamic oil film for lubrication whilst the shaft is rotating, so avoiding metal-to-metal contact. The ability to produce the hydrodynamic oil film is governed by the peripheral speed of the shaft, the thickness or viscosity of the oil and the load on the shaft. The load is carried by the oil wedge. The casing which holds the bearing can either be cast or fabricated steel, and is split on the horizontal joint, allowing easy access for maintenance.

Because the load is downward there may only be a white metal bearing in the bottom half of the casing, although complete bearings are also fitted Figure 1. Another type of bearing that works on the sliding surface principal has a bottom half bearing which is divided into three sections.

These bearings have a pivoting pad mechanism which allows the bearing to tilt when the hydrodynamic wedge forms, and in theory will support a greater load. Conversely a smaller bearing area is required for the same load. Once again a complete bearing can be provided depending on its application Figure 2.

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