PRV installed downstream line of the Metering pump? 1

[silebi66]

The Metering pump is used for chemical dosing (NaOH).

Is it ok to installed PRV(upstream pressure control)on the discharge line of Metering pump for chemical dosing ?


My boss told me that the back-pressure regulators (Upstream pressure control) will be close to shut off the valve when the upstream pressure fails so it can protect the downstream vessel not to be contaminated by NaOH.

But, others senior think it is not necessary to install PRV to contorl the upstream pressure (cost increase), and also the metering pump is operated in constant pressure so it doesn't make any sense to
control the constant pressure pump.


Any comment and help will be highly appreciate.

Thanks.

 

[bimr]

Back Pressure Control Valves
Many metering pump applications dispense to atmospheric conditions or into a process with less than 20 psig pressure and more typically, into a process with erratic system pressure. These applications require back pressure to ensure a constant pressure for the discharge check assembly on the metering pump to work properly. It is crucial that Back Pressure Valves such as TOP VALVE be installed in the discharge piping of the pump to ensure a constant pressure for the discharge check assembly to work under. This allows for the repeatability of a constant fluid discharge per stroke, and accuracy desired. Additionally, TOP VALVE back pressure valves automatically provide anti-siphon protection and are available in a variety of sizes and materials.

Other than the above, it is not clear exactly what you are doing. Since you are pumping a potentially hazardous material, it would be wise to make sure what you are doing is correct. Perhaps you can post a flow diagram sketch or consult with the pump manufacturer.

http://www.primaryfluid.com/optimize.html

 

[JJPellin]

bimr, I could not have said it better. Well done.

Johnny Pellin

 

[silebi66]

Thank you very much for bimer kindly to give us a very clear explanation.

I might not fully comprehend the process issue on the reciprocating pump.

The following is my query :

The discharge rate will pulsating periodically for this pump, so the PCV valve will pulsating on its set point,

therefore, it can't make this pump or process condition stable.

And, the allowable differential pressure for PCV is much smaller that other common control valve, so it might not

work properly if the high purity product is to be required to generated downstream vessel.


Please correct me if I wrong on this point.

Thank you very much.

 

[bimr]

The PRV allows for the repeatability of a constant fluid discharge per stroke, and accuracy desired once you have maintained the minimum backpressure. You are using a metering pump that passes a defined volume on each pump stroke.

The discharge pressure is not generated at the pump; it is generated from the backpressure in the piping. Even though the pressure in the line fluctuates, since the metering pump is a positive displacement pump, the pumped volume over time will be accurate.