Sizing a regulator

[skuntz]

I am sizing regulators (Fisher, specifically) Their technical bulletins give guidance such as IEC constants for sizing just as you would any other valve, but they also provide data for calculating "wide open flow for relief valve calculations". I do not know what this means. Is this the maximum flow in normal operation or is this a special condition. Is there something I am missing about sizing a regulator? I was assuming that you would treat it as you would any other valve.

 

[rmw]

If you size a regulator properly, it should not operate at or near wide open. It would be a poor sizing job.

However, some regulators are used as back pressure regulators that function almost like relief valves and it might be handy to know the full open flow characteristics of the valve for such a condition.

I like my valves and regulators to work in the 60-80% open range normally. Find your "sweet spot" and size your regulator to operate there and run a set of "wide open" flow calculations as a "Bravo Sierra" check and hope you never have to operate there.

rmw

 

[psafety]

"wide open flow for relief valve calculations" is exactly that a VERY IMPORTANT number. This is the worst-case failure rate that the valve will pass. The vessel/tank etc should have relief capacity for this rate based on its rated pressure. This has nothing to do with operation.

 

[rmw]

psafety,

That may be a good point. Frankly, I am not accustomed to thinking of a regulator as a relief device. The tanks and vessels I deal with have their own dedicated single purpose relief valves for that purpose. I have put regulators on vessels that had a relief valve but not wanting to be popping the relief valve constantly, I sized the regulator to do the job instead of the relief valve when it could.

The regulator however normally did not operate in "relieving flow" but in back pressure regulating flow which weren't the same thing. Since its primary job was back pressure control, the sizing was optimized to controlling that flow.

rmw

 

[skuntz]

So then what you are saying is that for normal operation, I would treat sizing the same as any other valve, correct? I ask the question because Fishers sizing program (Fisher Specification Manager) does not include their regulators.

 

[moltenmetal]

Self-operated regulator sizing is based on how much "droop" you can tolerate, i.e. the precision of setpoint maintenance you need at the highest expected flow.

The full open flow number is used for sizing downstream relief devices which serve to protect against the full-open failure of the pressure regulator.

 

[steamdog]

I am a Fisher Representative and size these regulators all the time, mostly using the flow charts rather than doing the hand calculations. Molenmetal is correct, the 'wide open flow' number is used strictly to properly size the relief valve.

Why not just call your Fisher rep, they are sure to help, this is sorta our job...

 

[skuntz]

Steamdog,

Actually I do deal with a rep, but our client limits who we can talk to about my project & I can't always get a response before I need an answer. Frequently then I need to come up with the calcs on my own.

Since you are a rep then maybe you can tell me - why has Fisher dropped their "FirstVue" regulator sizing program?

 

[steamdog]

Skuntz,
Firstvue was stopped because Fisher moved to a new internal sizing program, and the internal and external programs needed to match up. They now have a customer sizing program called 'Fisher Specification Manager'. The link is below.

However, I do not use this but the internal program that is also a pricing and ordering tool. I looked at the brochure for this new program and it mentions control valves but not regulators. Regulator sizing should be in there but I am not 100% sure.