627 Regulator - Flow capacity lower at max inlet pressure? Why? 1

[SlavaU336]

Hi Everyone,

Question: How come for a 627 regulator for example, if we reach the maximum inlet pressure than the trim size can handle,
how come the flow capacity at the max inlet pressure is way less than the flow capacity with an inlet pressure that's half the max inlet pressure?

Example: Table 9 - Type 627 Capacities for NPS 2 body size and orifice size = 1/2 in - Outlet Press = 60 PSIG; Inlet pressure: 300 PSIG => Capacity = 79,000 SCFH. For the same regulator, same outlet pressure, if inlet pressure = 750 PSIG => Capacity = 32,000 SCFH. Thanks for your help!

Picture of what I'm talking about:

https://files.engineering.com/getfi...25d4701&file=Screenshot_2023-08-18_113133.jpg

 

[LittleInch]

Something a bit odd at the end of those tables.

But in general nax flow increases with inlet pressure

Sonic velocity?
Noise?

Ask the vendor.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GBTorpenhow]

This is something of a guess but I suspect it has to do with controllability. The capacities published are at some % droop so even if at higher pressures more gas can be shoved through the orifice it might not be controllable to a set point within X% of set pressure at those flows. The larger orifice would probably make it harder to control as inlet to outlet pressure ratio goes up, just in terms of the gain on the device internals.

 

[1503-44]

If you download the Fisher calculation manual, they say an excess relief capacity is required at high pressures and do a Q2 calculation and subtract that from Q1. Rather than size the valve for an excess capacity required, they seem to reduce the allowable capacity of the valve that is being checked.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."