a quick approximate on site estimate is required, it should not be applied to high specific speed pumps such as vertical turbine or mixed flow pumps, whose power curves can follow significantly different rules.
DRoP tEst
This is the least accurate method, and requires knowledge of sump dimensions and levels. It is often used on sewage pump installations, where sump emptying occurs over a relatively short period of time.
In this method, the time taken for a pump to lower the sump level over a known depth is recorded. The volume of liquid pumped is then calculated based on the sump level change and the sump area, and is divided by the time taken to arrive at a volume flow rate.
For example, if a sump has dimensions of 4m x 3m, and the level is reduced by 1m over a time period of 10 minutes, the average pump flow is (4 x 3 x 1)/10 = 1.2 m3/min, or 72 m3/h
This method has a number of inherent inaccuracies:
• During the drop test, it is likely that flow will continue to enter the sump. This will affect the result – the extent of the effect will depend upon the rate of inflow in proportion to the outflow.
• The sump may not have a uniform section, making volume calculation less accurate.
• As the level is lowered, the total head on the pump changes which will affect the pump output. Any resultant calculation will only give an average flow over the range of heads.
• Measurement of pumped depth may be difficult if there is no installed measuring equipment.
sUCtIon PREssURE MEasUREMEnt
In most pumping stations, it is possible to obtain a pressure reading on the suction side of the pumps. The velocity and friction head components of this reading can be used to estimate the flow. To use this method, it is necessary to know the pressure drop on the pump suction (static suction pressure - operational suction pressure), the type and number of pipe fittings up to the pressure measurement point and fittings diameter. An estimation of the fittings friction (K) factor is also required.
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Convert the suction pressure drop (P in kPA) into a head drop (Zd in meters) using the equation:
Zd = P x 0.102 sg
(note that this Zd calculation will change depending on your site measured units) Obtain a total K factor for the suction fittings up to the measurement point. Assuming there are no significant straight pipe losses in the suction, the following equation can then be used to determine the flow velocity:
Zd = V2 x (1+K)
2g
Once the velocity is known, the flow rate can be calculated using the suction diameter. This method can be adapted to suit a wide variety of suction and pump configuration and the available locations for pressure measurement.
Although there are potential inaccuracies in determining K factors and internal diameters, careful use of this method can allow the velocity to be estimated to within a few percent.
ConClUsIon
There is no single simple and accurate method of determining flow in systems where installed meters are not present, or where the use of alternative temporary flow metering equipment cannot be fitted. Instead there are a number of methods that can be utilised to obtain an approximate pumping rate, which in many cases may be sufficient for the purposes required.
All these methods have limitations and inherent inaccuracies. Where these methods need to be employed, it is worthwhile applying at least two methods to get comparative results.
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sECtIon 9
aPPlICatIon Do’s anD Don’ts suction & Delivery Piping
Ensure that bolt grouting or chemical anchors are allowed to dry thoroughly before connecting any pipework.
Note that fire pumpsets have regulatory requirements for piping and these must be strictly observed. Refer to the appropriate standard for details. Both suction and discharge piping should be supported independently and close to the pump so that no strain is transmitted to the pump when the flange bolts are tightened. Use pipe hangers or other supports at intervals necessary to provide support. When expansion joints are used in the piping system, they must be installed beyond the piping supports closest to the pump.
Install piping as straight as possible, avoiding unnecessary bends. Where necessary, use 45º or long sweep 90º bends to decrease friction losses.
Eccentric Reducer on a Split Case Pump
Typical End Suction Pump Piping Installation se Cti ON 9 PUMP sPECIFIC at Ion an D oPER at Ion Contents 3 4
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Make sure that all piping joints are airtight. Where reducers are used, eccentric or ‘flat top’ reducers are to be fitted in suction lines and concentric or straight taper reducers in discharge lines. The length of eccentric reducers should be about four times the pump suction diameter. Undulations in the pipe runs are also to be avoided. Failure to comply with this may cause the formation of air pockets in the pipework and thus prevent the correct operation of the pump and measuring equipment.
The suction pipe should be as short and direct as possible, and should be flushed clean before connecting to the pump. For suction lift applications, it is advisable to use a foot valve. Horizontal suction lines must have a gradual rise to the pump. If the pumped fluid is likely to contain foreign matter then a filter or coarse strainer should be fitted to prevent ingress to the pump.
The discharge pipe is usually preceded by a non-return valve or check valve and a discharge gate valve. The check valve is to maintain system pressure in case of stoppage or failure of the driver. The discharge valve is used to prevent back flow when shutting down the pump for maintenance.
CoUPlIng alIgnMEnt
Periodical checks of shaft alignments should be undertaken and if necessary adjusted accordingly. In order to maintain the warranty status of your SPP pump it is recommended to take out an SPP preventative maintenance contract. SPP’s field service engineers have extensive experience in pump and coupling alignment. Refer to the pump and coupling
instruction manuals for details of shaft alignment procedures and tolerances or proceed generally thus: a) Lateral Alignment
Mount a dial gauge on the motor shaft or coupling with the gauge running on the outer-machined diameter of the pump coupling. Turn the motor shaft and note the total indicator reading.
b) Angular Alignment
Mount a dial gauge on the motor shaft or coupling to run on a face of the pump coupling as near to the
outside diameter as possible. Turn the motor shaft and note the total indicator reading at top & bottom and each side.
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