External downstream pressure switch

[a1987]

Dear Sirs

for several gear pumps, on process data sheet is present the indication of an external downstream pressure switch...and for those pumps is not present the indication for internal relief set..

i think internal relief valve should be provided and its set pressure too, regardless external downstream pressure switch..

what do you think about?

 

[Artisi]

Sounds reasonable, think you need to be able to monitor and set the discharge pressure independent of the downstream pressure if fitted the discharge is fitted with any pressure control valve.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[a1987]

ok, thank you... think that those pumps are moved by a VFD.. this info changes anything?

 

[LittleInch]

Not really IMO, and I think we are all in agreement, but it all depends on whether there are any isolation or control valves between the pumps and the Pressure switch and how much you trust your control system to work. Gear pumps and most PD pumps can generate large over pressures before the motor stalls so, again IMO, unless you have a 2oo3 (two out of 3)pressure voting system with a suitable high rated shutdown and trip system (SIL3), you really don't have a plan B if your pressure switches or control system don't work as intended unless you have a PRV on the discharge line BEFORE the first downstream isolation valve.

Still seems a bit like a false economoy to me and if some pumps have them and others not, there is always a danger that in the future one without internal PRV could be swapped for another with it on the same plant without anyone realising.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Artisi]

gear / positive displacement pumps are not my field of expertise but think you should be able to monitor and set either shut-down or a relief valve against over pressure to safeguard the pump - unless of course the pump has pressure relief built-in.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[DRWeig]

LittleInch,

By IMO, are you referring to the Colfax IMO pump? I can't quite follow your sentences if so...

Best to you,

Goober Dave

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[LittleInch]

Sorry, I thought that was eng-tips approved abbreviation for "In My Opinion"...
;-)


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way