Dosing pumps in practical applications
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ng diagram illustrates these conditions: (Figure 7)
Output diagram of a diaphragm dosing pump
• Required capacity: 100 l/h (26.4gph)
• System pressure fluctuates between 2 and 6 bar (29 to 87 psig).
The capacity will be adjusted via stroke length ‘a’ to 100 l/h (26.4 gph) at 6 bar (87 psig). If there wasn't a pressure loading valve installed and the system pressure dropped down to 2 bar (29 psig), the dosing pump would discharge 110 l/h (29 gph), which is too much. With the installation of a pressure loading valve that is pre-set to a pressure of 7 bar (101.5 psig) the pump's stroke length has to be adjusted to ‘b’ so that it discharges 100 l/h (26.4 gph).
If the strike length setting remained at ‘a’, it would dose only 90 l/h (23.8 gph). With the pressure loading valve adjusted to a certain resistance the diaphragm dosing pump will discharge 100 l/h (26.4 gph) against 7 bar (101.5 psig). However it must be remembered that the pump does not realize that the system pressure fluctuates down stream of the pressure loading valve.
2. Avoiding siphoning
Some chemical feed systems are designed in a way that allows the potential of unregulated flow of chemical through the dosing pump. This so called "siphoning effect" may occur when the dosing pump feeds to atmospheric pressure (i.e. into a tank or a reservoir), while the supply tank is above the injection point. A pressure loading valve installed at the end of the discharge line and set at a pressure that is slightly higher than the hydrostatic pressure between the completely filled supply tank and the injection point eliminates the siphoning.
3. Dosing into vacuum lines
A dosing pump that is supposed to feed the chemical into a vacuum line or into the suction line of a centrifugal pump faces the danger of feeding more chemical than required. Here too, a pressure loading valve that can not be opened by the vacuum can be helpful. Process liquid will be dosed, only when the valve opens, due to the pressure generated by the dosing pump.
4. Pressure consistency in circulation lines
In the process technology circulation lines are used to provide one media to several end users with the same pressure (Figure 8).
Flow diagram of "constant"
A pressure loading valve placed at the end of the circulation line keeps the media at the same pressure within the circulation line.
The pump has to be sized to accommodate enough output to satisfy the demand of a fully opened system. If not all end users re