Pilot Operated Vs Direct Acting Pressure Reducing Valves

[learner08]

Anybody knows the typical droop for both? Want to know this as would like to know if I am presented with both options, whne should I pick either or?

Been readind thru books and they only give qualitative criterias and not quantitative.

Thanks.

 

[Joesteam]

In general, direct acting valves have more droop than pilot operated. As a matter of fact, I have not seen droop associated with the pilot operated valves, as the Cv and flow for the valve is normally reported without ANY droop. For example, Spence regulators report a 1 psi accuracy at 95% of rated flow.

For direct acting valves, each manufacturer rates thier own valves, so there is no typical. In most cases, they have a different rated Cv's for the valve according to the amount of droop that is acceptable to the end user.

For example the valves I am familiar with are the Leslie GPK. for a 3" valve they report a Cv of 55.8 with 2 psi min. droop and a Cv of 84.6 for a 3.5 psi min. droop.

It is similar with Cashco direct acting where they report an entire chart of Cv's with 10%, 20%, and 30% droop.

I don't know if this helps...