If main and standby pumps are operating in a hot liquid system , consider bleeding a small amount of discharge flow back through the non-operating pump to keep it at system temperature. Be careful to avoid pressurization of the system suction side. May 1999- Do not expose a cold rotary positive displacement pump to hot liquids nor visa versa. Internal pump clearances cannot change uniformly very quickly and such operation risks pump seizure. Especially avoid cold liquid flush of a batch hot liquid pump.
Thermal shock can cause serious pump damage.
Soft start is most commonly achieved using an electric motor driven, open bypass valve around the pump or back to the supply tanks. Other soft start systems have used fluid couplings for slowly increasing pump speed as the pipeline can accept flow or other variable speed drive arrangements. Dry running most pumps can cause damage, if to nothing else, then at least the shaft seals. 28 May 1999- Pipe strain can be particularly hard on rotary positive displacement pumps as their internal clearances are smaller than centrifugal type pumps. Close running clearances may require alternate seal flush arrangements.