What will be adverse effect on pump if someone operate centrifugal pump with lower density fluid than specifie?
Due to the lower density the pump will have a slightly lower load on the motor and the discharge pressure will be lower by the ratio of the two densities. There is no reason to expect the speed to change unless the pump has a variable speed driver and is controlled by the discharge pressure. With an electric motor driver, the speed will remain constant. There could be some problems with the seals or packing if they are not designed for a fluid similar to LPG. The efficiency should remain the same. The seal manufacturer can tell you if the existing seal will be a problem. A properly designed pump will not have any metal to metal contact during normal operation so that should not be a problem. Only if the pump is a vertical turbine pump with bushings along the shaft could this be a problem but that is not likely since they should be bronze or some other material different from the shaft material.
