If I design a sewage collection system using pressure pumps in series, do I need check valves in each?
June 2nd, 2009 | 
Author: individual station, or are centrifugal sewage pumps designed to withstand back flows without a check valve?
It depends on the construction of the pump as to its ability to rotate backward but in general they can rotate backward to some degree with no problem. If the pump is large and has a pressurized lube system, then it might be a problem
One problem with a pump running in reverse is the lack of any speed control. It is possible for the pump to exceed one of its design parameters in that case.
It is generally considered good practice to put a check valve in the discharge of any centrifugal pump that might run backward or over pressure the suction if the driver fails. A fully opening swing check would probably be the best choice for this application. It may not always fully close but even a leaking check valve can provide some protection.
An automatic closing ball valve is probably a better choice if the actuator is set up to fail closed, but that type of system requires careful study to be sure it functions in a safe manner.
Posted in Pressure Pumps
That would depend on the operation of the station. Is it in operation all of the time, or only as needed? Another point is the question of sump capacity, and "on demand" switches with some kind of level detection system. In that case, also provided that back flow is not an issue, then a check valve would not be needed. A problem with a check valve would be material in the waste that could keep the valve open, even if only a little bit. This would destroy the intent, and function of the check valve. In systems that I have seen, check valves are not used. I would not use a butterfly valve in a waste system since material in the flow could block closure operation. I would use either the ball valve built for that service, or a bladder type valve. The bladder valve uses a "balloon" that can be inflated as needed to control the flow. Water filter plants use this type of valve for some applications.
References :
It depends on the construction of the pump as to its ability to rotate backward but in general they can rotate backward to some degree with no problem. If the pump is large and has a pressurized lube system, then it might be a problem
One problem with a pump running in reverse is the lack of any speed control. It is possible for the pump to exceed one of its design parameters in that case.
It is generally considered good practice to put a check valve in the discharge of any centrifugal pump that might run backward or over pressure the suction if the driver fails. A fully opening swing check would probably be the best choice for this application. It may not always fully close but even a leaking check valve can provide some protection.
An automatic closing ball valve is probably a better choice if the actuator is set up to fail closed, but that type of system requires careful study to be sure it functions in a safe manner.
References :
If you put centrifugal pumps in series, the pressures add up so you might not want to do this unless your pumps are spaced a great distance.
It is common practice to put a check valve on the discharge of any pump including a centrifugal pump or you will get flow backwards thru a centrifugal pump.
References :