Determining System Design Pressure

[Yamahauler]

I need some advise on determining the system design pressure of a water treatment system. Water is required to flow at 150 gpm through a series of filters. The total head loss is ~130 psi. The filters are pressure vessels and I need to maintain a min. of 10% between relief (design) and operating pressure. I was wanting to go with a 150 psi design pressure (and relief setting), but I'm afraid I'm too close to my operating pressure. My assumption is the 130 psi head loss would be my operating pressure. Am I correct? Should I go to a 300 psi rated system?

Thanks in advance!

 

[bimr]

No, not really. There are a number of ways to do this, but you have not provided all of the information that is required to make an intelligent decision.

What is the maximum pressure of the pumps feeding this system?
What is the pressure that your system is maintaining on the discharge side?

It is common practice to make the design pressure of the tanks greater than the maximum pressure of the pumps feeding the system. That pressure would be called the system design pressure. Your entire system including piping must be designed to take this pressure. Since, your tanks will then be rated at a higher pressure than normal operating pressure, you do not have to worry about providing full pressure relief.

The operating pressure will be different for each of the filters in your filter system. But, the design pressure will be the same for each filter.

A reasonable system design pressure is 125% of the maximum pressure of the pumps that will be supplying the fluid to your system.

 

[Yamahauler]

Thanks for the reply. To answer your questions...

1. I have not specified the pumps yet, we are trying to spec the filters first.

2. the system will discharge into a holding tank at atmospheric pressure.

 

[davefitz]

Bimr has good comments.

Also, it may sound elementary, but a 150# nominal piping and flanges are actually suitable for significantly higher pressures than 150 psig. For example , for carbons steel pipe and WCB valves a 150# system at 200F is suitable for a 240 psig design pressure.