We have a situation where we operate three horizontally split case centrifugal pumps that are connected to the same suction line and discharge line. When operating under suction mode, the gland packing are known to leak air into the system. Usually it's one pump duty and two of the pumps on standby.
I have been told that to prevent air leak into the system, a flushing line that bleeds water from the pump volute and provides pressure on the packing gland can be installed. This should solve the air leak through the duty pump. However air would still leak into the pumps through the packing gland of the standby pumps.
Hence, i am thinking of mechanical seals on all three of the pumps. My question is how good are mechanical seals under very low or vacuum condition? Would low pressure in the pump push the two faces apart to leak air into the system?
Thanks for any information