Standby pump suction pressurized

[fdomin]

Have you ever seen the suction of a standby pump being pressurized up to the discharge pressure of the running pump?

Could this happen if the standby suction line is closed and its discharge line open, regardless of the check valve presence?

In this case rating of suction side instruments (low flow & pressure switches) should be that of the discharge side?

Regards,

 

[BigInch]

Sure.

Don't know.

And the suction flange pressure rating must also equal the discharge flange rating.

"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization

 

[fdomin]

Thanks BigInch.

Now the question is why most pump systems have their suction side designed according to max suction pressure and not discharge pressure.

Can we regard on operating procedures to avoid increasing suction rating?

 

[BigInch]

Because they usually don't need it, but for example these two scenarios could easily cause very high pressures at suction,

If you have two equal pump stations connected by a flat pipeline, a shutdown of the second's discharge pipeline while the first keeps running will cause full dischare pressure of the first station to reach the second pump station's suction line.

A recycle line from a pump's discharge line back to its own suction line might easily cause suction side overpressures when the recycle line's valve opens too much.

If you can have these or a similar scenario, you must protect a lower rated suction flange by a relief valve, or upgrade the suction inlet to equal that of the discharge side. Its important to specify the maximum possible suction pressure that can reach the pump. On smaller units, both suction and discharge ratings could easily be the same, but its not always the case for large power units. I've had pumpswith maximum suction pressure ratings equalling only 1/4 of the discharge pressure rating.

"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization

 

[Artisi]

Big Inch- I love that quote from Mahatma Gandhi - subtle as a sledge-hammer.

 

[BigInch]

Been keeping your head down?
Please try to stay out of trouble.

"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization

 

[Artisi]

The problems, as in violence, being shown in the western media are isolated cases but never the less a worry especially if you are involved as a peaceful demonstrator which 99.9% are. The politics or lack thereof are of more interest but as a westerner very difficult to follow - what is black today could well be red or even blue tomorrow - depends on who is doing what to whom and who the who is.

 

[BigInch]

Good. Just take care. Peaceful can turn ugly in a few milliseconds. Usually not in the millisecond you are expecting.

fdomin, Sorry for the hijack, but that was important.

"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization

 

[BillBirch]

fdomin,
This commonly crops up during HAZOPs of manifolded pumps generally leading to suction flanges and inlet block valves being uprated to discharge ratings. It is usually caused by anticipated leakage back through discharge check valves.