Dosing pumps in practical applications
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d during the pump's discharge stroke that will be released back into the pipe system during the suction stroke. Depending on the system design, pressure oscillations are mostly reduced and the flow is leveled. Installation of the PDS in line with the pipe ensures constant flushing. Optimum results are achieved if installed close to the dosing pump. The installation of the PDS is possible on both sides of the dosing pump, on the suction as well as the discharge side. Certain applications are possible, when a PDS is applied. I.e. a PDS on the pump's suction side improves the fluid dynamics, thus cavitation is avoided.
Another opportunity to apply a PDS is when a flow meter is implemented. Most flow meters cannot be used on the discharge side of a dosing pump without additional modification, because the float would move up and down too fast. When a pulsation dampener is installed in short lines or pressureless applications, an additional device (orifice or needle valve) has to be incorporated in order to optimize the PDS' operation. If the flow has to be measured in high pressure applications, the flow meter should be installed on the dosing pump's suction side with the PDS behind the flow meter.
Operating conditions
Diaphragm valves are the preferred option as pressure loading valves. They are tightly sealed (to the outside) and offer safe operation, due to their sturdy. Pressure loading valves are applied mainly for four reasons:
1. Generation of an artificial pressure load for dosing pumps
The capacity of a diaphragm dosing pump is pressure dependant. If the pressure in a chemical feed system is fluctuating (i.e. 2 ... 6 bar / 29 ... 87 psig) in a potable water line, it is of advantage to install a pressure loading valve that will provide the diaphragm dosing pump with a consistent back pressure that is always higher than the highest expected pressure in the dosing system.
Here the pressure loading valve should be set at 7 bar (101.5 psig). The pressure loading valve works as an anti-siphoning device and doesn't allow the pump to discharge at any pressure below 7 bars bar (101.5 psig). The pump must always generate a pressure of 7 bar (101.5 psig) in order to push the process fluid through the valve, even at low pump capacities. Even with fluctuating system pressure conditions the dosing pump always sees a consistent back pressure of 7 bar (101.5 psig) and will work according to its design criteria. The followi