I am a french process engineer working in an Engineering Company.

My problem is that the piping engineer asked me the following data for a number of non-return valves:

- The min. and max. flowrates
- The min. and max. operating pressures
- The min. operating temperature
- The minimum pressure drop (for opening)

It is the first time i am asked this but i have found some data. For example, i have considered the design conditions for the max. conditions (flowrate, pressure). However i have some doubts concerning the definition of the min. conditions and the min. pressure drop.

Before asking the piping engineer more precisions, i was wondering if you could help me clarify some points, namely:

1/ Does the min. flowrate correspond to the min. operating flowrate or the min. flowrate for full lift?

2/ What is the purpose of min. pressure? Can i consider the atmospheric pressure (0 barg) or the full vacuum pressure (-1 barg) which could occur during start-up, shut-down or maintenance?

3/ What is the purpose and how to calculate the min. pressure drop? are there some typical values by type of valve?

If you have interesting references, please feel free to share.

I am a piping material engineer.

Followings are my answers,

1. min. operating flow rate
2. this question is for the mechanical design of valves.
   therefore you should give him/her the most severe
   condition. Then valve vendor will consider it.
3. Why did piping guy mention "(for opening)"?
   If he wants the min. pressure drop for opening,
   that is for the cracking pressure, which is the minimum
   required pressure for valve opening.

I guess this valve is not normal check valve.....right?

I think your problem and our problem is that we do not exactly know what your piping engineer is looking for. Does he want to have information regarding the valves OR information regarding the process?

1) Regarding the minimum flowrate I would say that the process is prevailing. Your system will determine the flows going through a valve. The valve suppliers just have to make sure that they can handle the required flowrates. Do not use the flowrate for full lift, since this is different for each valve type/make.

2) Again this is a process question. You determine the pressure range you want. Minimum pressure is normally atmospheric pressure. But if your process will have close to vacuum pressures you should define that.

3) Depending on your system you can determine the maximum allowable pressure drop. Based on the available upstream pressure and the required pressure downstream in your process. You should probably do this together with the piping engineer, because your piping, bents etc. will influence this. The next step is to find a valve design that has less pressure drop than the maximum allowable pressure drop. A different valve design or valve make will have a different pressure drop. In general an axial flow non slam check valves will have the lowest pressure drop. Normally the valve suppliers will calculate the pressure drop for you if you give them the process conditions (flow/medium type/medium density/pressure/temperature).

You are the person that determines the conditions that your check valves has to comply with. The check valves do not determine your system.

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