Discharge side check valve for centrifugal slurry pumps
Discharge side check valve for centrifugal slurry pumps
(OP)
We were told today that we should use check valves on the discharge side of our slurry pumps to prevent possible (major) damage. We have relatively large (6,8 and 10 inch discharge diameter) pumps, discharging to 10, 12 and 16 inch diameter 30 feet high discharge manifolds. The calcium sulphate and calcium carbonate slurries we use are higly abrasive, corrosive, and tend to stick everywhere, so I assume that´s the reason why check valves weren´t installed in the first place (we do not even have discharge side valves in some of the pumps, but that can be solved easily). Are we really risking major damage to the pump in case of, for example, the impeller back-turning after a power failure because of the 30 feet discharge side water column, and somebody turning the pump back on while it is still backturning? These guy who recommended the check valve supplies the mechanical seals for some of our pumps, and he says that even the seal could be damaged by the water hammer (?) effect. Any comments will be very welcome. Thanks..





RE: Discharge side check valve for centrifugal slurry pumps
Mark McLean
WorleyParsons
RE: Discharge side check valve for centrifugal slurry pumps
Any analysis should be part of a risk management assessment. What is the likelihood of a power failure or hitting of an emergency stop? What are the consequences of losing one pump? DO you have a standby?
If you go to www.pipingdesign.com there are two papers there on surge. You will find my contact details on them.
If you need a check valve to protect the pumps the Duckbill type by RED valve are a good but costly selection for slurries. They will cope with very abrasive slurries.
Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng
www.waterhammer.bigblog.com.au
RE: Discharge side check valve for centrifugal slurry pumps
RE: Discharge side check valve for centrifugal slurry pumps
1. How long have we operated these pumps without check valves on the discharge?
2. Have we ever experienced any problems?
3. What happens now when you shut-down the pumps under normal operating conditions?
4. Has there ever been any water hammer?
If you have never experienced any problems;
5. Why change the operating system now?
Furthermore, having the pump driven backwards by flow from the discharge will NOT unscrew the impeller.
If there is a chance of the pump starter being activated while the pump is still running backwards, simply put a delay timer in the control system set for a measured delay period.
Naresuan University
Phitsanulok
Thailand
RE: Discharge side check valve for centrifugal slurry pumps
What is not very clear to me is how could a significant water hammer effect happen in my system if a pump shuts down and backturns for a few moments until the discharge column is depleted. Our system is pretty straight forward, tank and pump are both at floor level, and have a simple 30 foot high discharge manifold which discharges via control valves to a scrubber at atmospheric pressure levels, no other high pressure generators involved. I read the papers suggested by stanier (thanks by the way stainer, very good references), but I still can´t visualize a significant water hammer in my specific case. Any references that talk about water hammer effects in simple pump applications with a not-to-tall discharge manifold such as ours? Thanks again.
RE: Discharge side check valve for centrifugal slurry pumps
Have you experienced any waterhammer effects in your system? Normal SCADA instruments do not have fast enough transducers to pick up pressure transients.
In respect of slurry pumps with hard iron impellers these are fixed by threading the impeller on the shaft. I have seen the impeller screw off and jam against the pump housing. But that was because the spaarky had wired the motor the wrong way and the commissioning engineer didnt check the direction of rotation before fitting the vee belts and aligning the pulleys. I have heard of pump impellers unscrewing due to water hammer but these have been on long pipelines that reverse flow through a forward rotating pump where the check valve had failed.
There are two types of damage from waterhammer. One is catastrophic-linebreak, pump impeller coming off. Risk assessment possibility =??? Consequences=???? Your call.
The second is repetitive fatigue damage. Likelihood based on number of stops=???? Consequences of losing one pump so it can be fixed depends on having a standby or not and how busy your maintenance people are, increased maintenance, cost of spares=??? Again your call
Paraphrasing the Mastercard advertisement in Australia at the moment:-
A surge analysis of your system for one pump would cost= < $2000.
Cost of check valves would be = $4-16000 per pump + installation. Even more if production is lost.
Cost of a good night's sleep and not losing your job= Priceless.
Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng
www.waterhammer.bigblog.com.au