Pressure Regulator

[ab12cd]

We have got a 1000L vessel with a vent. The vessel design Pressure is 4 barg. We pump liquid into the vessel using a diaphragm pump which is operated by using compressed air at greater than 5 barg. The pump has a relief valve set at 7 barg, to protect the pump. I believe a pressure regulator will be required, set at 4 barg since liquid is being pumped into to the vessel at a greater pressure than the design pressure of 4 barg but am not sure about this?

 

[EGT01]

First, don't confuse a pressure regulator as a substitute for a pressure relief valve. If you are concerned about your pump possibly overpressuring your vessel, then that should be an additional case to be considered for your vessel's relief valve sizing basis. Even with a pressure regulator, it is typical to consider a pressure regulator failed or malfunctioned in the open position as a sizing basis for a pressure relief valve.

The need for pressure regulation will depend on your process requirements for delivery of liquid from the pump and how you are operating the pump with the tank. If the pump is operated on/off style to fill a tank with an open vent, I think you would not need a pressure regulator.

Considering a diaphragm pump as a positive displacement type pump, the stroke length and pump speed will determine the volume delivered. Then the dynamic loss, static head difference, and destination pressure will set the pressure at any point between the pump and destination. The pressure at the pump will be greater than the pressure in the tank otherwise you would have no flow.

What may require the need for pressure regulation is if you operate your pump continuously and try to throttle the flow, then you may want a pressure regulator system that would return flow from the pump discharge back to where you are taking suction. Obviously, you would want the regulator set so as not to exceed some max allowable pressure but also set low enough to prevent lifting any relief valve as well.

 

[TrevorP]

I'm not sure I fully understand the question, but the basic premise is that you don't want to overpressurise your vessel. This therefore requires you to have adequate pressure relief. You mention that the vessel has a vent, but you don't say whether you have an open vent, or whether it is pressure relief protected. If it is an open vent that is adequately sized for the inflow from the pump, then you don't need a pressure relief device, because, in essence, you have one. You may overfill the vessel, but that is a different issue.
If, on the other hand, what you are trying to do is to stop a relief valve on the vessel at 4 bar from lifting, then I suggest you put a relief valve from the pump discharge going back to somewhere on the suction side of the pump. A pressure regulator on the fluid would do a similar job, but is likely to reduce your flow. A pressure regulator on the air would similarly reduce the flow. On these type of pumps, a low air pressure will cause a substantial flow reduction.