Pressure Relief Valves.

[DuctHunter]

I have a quick question. I have a hydronics Rep telling me to put the pressure relief valve of a hot water system containing a heater exchanger on the suction side of the pump (right after the expansion tank).

Is this philosophy correct. Shouldn't it be on the discharge side of the pump where the highest pressure of the system is ??

Thanks for your response.

 

[ChasBean1]

Yes. Any safety device should protect the most vulnerable piping.

 

[willard3]

Why are you asking a salesman where to put a pressure relief valve? Find another Engineer where you work and ask him.

 

[DuctHunter]

Thanks for responding. The Rep happens to be a mechanical engineer that specializes in hydronics, pumps and hydronic accessories, and holds training seminars on such subject matters. So he is a qualified professional.

Having said that, our design showed the pressure relief valve on the discharge of the pump, but the contractor installed it on the suction side after the expansion tank. And to my surprise this hydronics engineer agreed with the location. My collegues at the office disagreed with the location and hence I turned to this forum for other opinions.

I wanted to see if there was a logic behind locating it there that I didn't quite understand or if anybody else agree with it.

 

[Compositepro]

The expansion tank controls the basic pressure in a loop and is the point where the pressure should be fairly constant. The tank is also likely to have the lowest pressure rating of any component in the loop, so it is what you are protecting. A centrifugal pump is self limiting in terms of pressure it can create and has no need for a relief valve.

 

[cjw81]

Should be at the point of least pressure change in system.

 

[Ziggypump]

Installing the pressure relief will give you a sort of false positive in the system pressure. Pressure will be greater at that point due to the pressure added by the pump. You always want to install the relief at the neutral point of the system with the expansion tank and air separater. This way the relief valve will open only when the system pressure gets too high, and not the flow pressure.

 

[yyj10]

Pressure relief valve release the builtup static pressure for safety. If you took a look of Bernoulli's equation, the pump discharge side has highest flow pressure, but not necessary highest static pressure. I agree with Compositepro, put it at somewhere the pressure is constant(low/no flow).