closed suction valve?

[mae1133]

What will happen to the discharge pressure gauge if you have a blockage or closed valve on the suction side of a centrifugal pump?

 

[LittleInch]

It will show a reduction in pressure.

Your pump will be busy cavitating itself to death so generally not a great situation to be in.

If your downstream system has a certain minimum pressure then that's what it will be reading after a short time.

Care to elaborate a bit further??

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

 

[mae1133]

We are starting up a system and apparently getting no flow from the pump and no increase in discharge pressure and low amps. I'm thinking the rotation may be reversed. I originally thought a blocked/closed suction, but upon checking the amps, I'm leaning towards a rotational issue?

 

[mae1133]

Further information coming in:

Rotation has been checked and the amps are 17amps FLA is 68. Suction is 4 psi discharge is 2psi.

 

[LittleInch]

Sounds like a blocked inlet to me. Wrong rotation normally gets you some flow, just not 100%.

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

 

[mae1133]

Yeah, that's what I'm thinking as well. Other thoughts is actually a broken shaft, but that would be highly unusual, especially in both pumps. Wouldn't a blockage in the suction cause an increase in amps though?

 

[LittleInch]

No because the pump isn't doing anything other than moving a bit of air around.

Are you sure someone actually fitted the impellors?

Or actually connected the motor shaft to the pump shaft?

Stranger things have happened on a new build.

You might have construction debris clogging everything up? Plastic bags are quite notorious.

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

 

[mae1133]

We are still checking things, but they say the impellers are installed. I'm getting them to check the static PG readings as well.

 

[mae1133]

Static Readings:

Suction: 4.5 psi on both pumps (This seems to be close to what the suction head of the tank is)
Discharge: 4 psi on one pump gauge and 3 psi on the other

So, when the pumps are turned on, the suction gauges go to 4 psi and the discharge gauges go to 2 psi.

 

[LittleInch]

Or are the impellors free wheeling?

No shaft key and nut fell off?

A bit odd the suction valves don't go lower than atmospheric though.

Any pump details you can share or p & Id?

I'm going for no impellor myself. Just the shaft whirling around.

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

 

[3DDave]

How much power was it supposed to take? If there's no impeller and just a shaft or if the impeller is loose on the shaft then there will be very low power required compared to what was expected.

 

[mae1133]

These are 75 HP ANSI centrifugal pumps with 12’ flooded suction and 33.5’ total static head. (2500 gpm @ 79' TDH)

 

[EdStainless]

Or a key was left out of the coupling and the impeller isn't turning at all.
Or the impeller isn't keyed to the motor shaft/nut loose or something like that.
Force them to tear one of these down with you there and document everything.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[mae1133]

I'm offsite, but have people in the field dealing with it. (Different side of the country) I'm just passing along things to look for or try.

 

[LittleInch]

Just let us know if they find anything - we all love a puzzle

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

 

[EdStainless]

But what I was driving at is that this needs to be documented.
If they come back in a few weeks and say everything is working fine with no other info I would be concerned.
I have seen maintenance guys take something apart, find the fault, 'fix' it, but not check to see if there was any damage from the earlier attempts.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[mae1133]

Not to worry, I will notify here of our findings. It will also be documented.

 

[Artisi]

The first question is always, is there anything to pump, wouldn't be the first time a blanking flange hasn't been removed?
2nd question, is the pump rotating?
3rd, is it correct direction?
4th. Has all air been removed from the casing?

If yes to the above, you have a problem

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.)

 

[RVAmeche]

Clogged start up strainers aka witch hats?

 

[georgeverghese]

Where is this suction PG - before or after the suction strainer?
Damaged gearbox?