We are developing a facility with which we want to calibrate cryogenic flow meters. As such, we have amongst others two tanks and a cryogenic pump which pumps from tank A to tank B. Tank A is located about 3 meters higher than tank B, the pump is directly below tank A.
The pump we have is a centrifugal cryogenic pump from Vanzetti, model DSM 230. For now, we are testing with LIN, however in the future we will operate it with LNG. We have used this pump without any (significant) problems one year ago. Recently, we have minimized our ambient heat by improving the insulation and now we are running into problems. The seal has been damaged and replaced three times (no real usage of the pump in between).
We cool the pump down for at approximately 4 hours after which we check the temperature and density of the LIN (density with Coriolis flow meter). When the lines are sufficient cold and density is sufficient high we turn on the pump. The problem is that initially the pump rotates smoothly (pump is manually rotated by hand trough the motor fan), however after a while it starts making some metallic sound. Also, there are some heavy points when you rotate the pump.
We have the impression that temperature may play a role; when the pomp is at ambient temperature it runs smoothly again without any noise. Can it be that the seal has become too cold? According to the manufacturer the pumphouse may get cold, however the motor and the connecting part between the motor and pump may not. This sounds a litte strange to me; a cryogenic pump that may not get cold. Furthermore, we use the pump-standy by heating.