Hi Guys,

Been reading about pumps vs. "pumperdrum" systems. I too would rather go for pumps. Unfortunately for me one of our clients has a "pumperdrum" system and thus have to work on it. A high maintenance animal to say the least!! The system uses H.P liquid subcooled through a closed flash tank to pumpwith majority of the time and when the level in the surge drum rises either when a room goes on defrost or so on pumps on hot gas once the float switch closes.

A few questions for the guys in the know:
Im sure they have a place somewhere.
1.) What are the energy implications using them on low stage compared to high stage systems? How would or what would the formulas be to equate these differences?
2.) What is the general NRV design for inlet/outlet on the pumping vessel?
3.) How safe are they really? they are constantly ranging between 0 bar - 3 bar every few minutes. Surely the vessel undergo stress.
4.) How would you design these vessel sizes on the required flow rate for the required load with a bit extra for future extensions? And.... Where would you fit your float switch on the drum for this?
5.) Horizontal or vertical and difference other than space requirements?

Your opinions would be greatly appreciated.
Out of intrest. Recently we found a problem with one drum not pumping efficiently. The problem being a bypassing vent valve on that drum. This caused a bigger problem for the compressor at the end of the line.. A bit of liquid carry over!!!!!
On further inspection we found the common vent line from the pumping vessels tied into a nozzle on the surge drum literally 200 - 300mm from the dry suction. Thus with enough velocity the subcooled pumping liquid vent through the bypassing vent valve into the surge drum and carried through to the dry suction line...
Luckily we had recently installed a "knockout pot" at the end of the line wich took most of the liquid...

We must always remember to keep our eyes open on site!!!!