Flanges when my Pump Shut off pressure is too high

[josetorero]

Hello,

I have a pumping system where my TDH is 140 meters (200 psi) . But my shut off pressure is 240 meters (340 psi).

I need to reccomend check and gate valves for my system. Should I use ANSI 150 flanges or ANSI 300 flanges?

See attachment

http://files.engineering.com/getfil...f-4e70-beff-16bc799bd240&file=Escenario_1.PDF

 

[pennpiper]

josetorero,
What is the Flange rating on the discharge of the Pump?

Sometimes its possible to do all the right things and still get bad results

 

[KoachCSR]

You need to select flanges (and other components in the system), based on your design pressure; Is your design pressure based on shutoff head or do you have overpressure protection in place to limit it?

Also, what is the design temperature of the system? In many cases at relatively low design temperature, ASME Class 150 flanges are suitable for ~300 psi design pressure.

 

[LittleInch]

Up to 100F, the rating of ASME (not ANSI) B16.5 Class 150 flanges is 285 psig.

Then, depending on your material and temperature the value can go down.

In your case, you are above the flange rating for something that is, in my opinion, a "normal" event and therefore you can't take advantage of any of the design code exemptions for occasional overpressure.

It would almost certainly be worth your while to find a pump without such a steep curve from operating point to shut off.

fix the cause, instead of trying to deal with the effect. There are many many pumps that do a similar duty out there without such a curve which based on your system curve (no 1?) you don't need as that is a very flat system curve - I kind of assume you're pumping water up a 140 high mine shaft?

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

 

[Artisi]

Why is shut head 240 metres, is this the pump shut head and if it is what will cause the pump to operate at this point?

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.)

 

[josetorero]

pennpiper, flange rating is ANSI 300

KoachSCR, this is a dewatering application, is just emtying a pond, there is no engineering behind it, so no design pressure has been calculated.

Artisi, shut off pressure is achieved when the pump is shutted down.

 

[LittleInch]

There is engineering behind it, just not developed a lot.

So what are you going to do?

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

 

[Artisi]

if total head is 140m how is it 240m when shut down -- are you closing a discharge valve and the pump is still operating?
more detail required.

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.)

 

[GD2]

Hi Josetorero,
LittleInch had directed you in the right direction. The max allowable working pressure for ASME B16.5 flange for A105 material is 285 pasig which will be less than the shut-off pressure of 340 pasig. You should use a 300# rating flange that will give you a max allowable pressure of 740 Psig. These pressure allowable are good up to 38 degree C.
The valves should also follow 300# rated valves if you are ordering ASME B16.34 valves. ASME B16.5 and B16.34 pressure ratings are almost same.

Ganga D. Deka, P. Eng
Canada

 

[KevinNZ]

Do need to have a valve on the pump discharge? No valve (or just an NRV) means the head should not exceed 140m. (But check for water hammer)