Is there a Difference?

I’m an engineer at a power plant 1 hour north of Baltimore. I was visiting your site and had a pump question.  My plant has 2 single stage liquid ring pumps.  They are rated for 30 scfm (we remove 6 - 8 scfm) and they have a hogging capacity of 700 scfm.  We have had our vacuum pumps fails 3 times in ten years.  Twice the impellors have broken. Once the impellor ripped through the pump casing; fortunately know one was injury.  A bad weld job was identified was the cause of one failure and cavitations was the other cause.  Currently, because of the water temperature, we are forced to run with both vacuum pumps.  We are looking to possibly purchasing another pump; however we need to identify the right pump for our plant. Our vacuum pumps are more or less meant to be hogging pumps (I think). We believe that our pumps are sized correctly, however one theory we have is that hogging vacuum pumps are not normally designed for continuous use; therefore our pumps have a short life span and that we should switch to two stage pumps.  Is there any truth to this?
It sounds like your pumps could be oversized, which is not a good thing
for a liquid ring pump. If it cannot suck enough gas the pressure will
go down and you can get cavitation. Your high water temperatures would
make the situation worse. I have also seen impellers come apart under
these circumstances.

It would be helpful if you could describe
the control system as this is another area where it is easy to go wrong.
I have found the technical reps from the suppliers to be very helpful
and knowledgeable and you should get their advice.
What is hogging? Peak load? If so, how can a 30scfm pump take 700scfm?

30scfm
pumps are very small and generally there shouldn't be any problem.
However, you can have a look into the following things, if it is a water
ring pump.

1. Casing should be totally drained before starting
the pump and you should let in water as soon as the pump starts. These
things can be accomplished by a automatic casing drain valve (just like a
check valve) and an automatic valve in the sealing liquid line.
2. Check for casing clearances.
3. Check the teflon balls of the discharge and suction valves. They might have got struck to their seats.
4.
Finally, check your maintenance records. If you hadn't touched them
except when they broke down, 3 times in 10 years is not unusual.

From the originalgatevalve
.