Lift Pumps

[jboy]

Can anybody please advise me on using a srew type pump as a lift pump. The question i need an answer to is probably a very basic one.
Would a Srew type pump pick up is own suction if it was to be sitting above a level of liquid, or would it need to be primed first? Is thisthe same with all kinds of pumps?
Also when priming a NEW screw type pump which has a positve suction head, should i expect to see the liquid bleed out of the discharge bleed, or would it not pass through the screw.

 

[jhelm]

Assuming you are talking about a positive displacement screw pump (as opposed to an Archimedes type inclined screw pump), the answer depends on the specific type you are using.

There are two, three and five screw type pumps that are all metal construction. These either use timing gears or, in the case of three-screw designs a film of liquid, to locate the rotating screws and keep them from grinding against one another. They can develop suction lift, but require priming by filling with liquid first. Some types may be able to pump some gas out of the suction. With all-metal screw pumps there are clearances between the screws, so liquid will pass through the pump easily.

Another type of screw pump is the single screw, or progressing cavity, pump. This uses a metal screw, or rotor, turning inside of a rubber stator that is molded to form cavities between the two. These have excellent suction lift capabilities due to the compression fit between the rotor and stator. To prevent damage to the rubber stator caused by heat build-up due to friction, this pump needs some lubrication when starting. It will, however, evacuate the gas in the suction line and prime itself if given adequate NPSH. The compression fit of the rotor and stator will hold liquid back when new at low pressures, but may allow liquid through if there is a significant positive head.

Generally, pumps are not intended to be used as valves and should not be relied on to prevent liquid from seeking its own level.

Air-operated diaphragm pumps can be used for suction lift without initial priming, provided the suction lift is within the capabilities of the particular pump.

 

A friend of mine used a helical rotor pump (a MONO pump with 316 stainless rotor and rubber stator)to draw bore water out of a dam on his property. The pump sat about 3m meters above the water level and it pumped a good flow to a tank about 200 meters up the property with about 6 meters to the top of the tank from the pump. He used a valve before the pump to keep the water in the line and then openned the valve before starting the pump to give it a prime. It worked fine for years.

The things I give away for free!!!!!!!

Regards,

Mike S

 

I'm wanting to know why ferrous alloys were use in sewage lift screw pumps. They rust, they're so bulky that they make maintenance difficult and expensive, and they're so huge as to make transport also expensive.

Why couldn't these things be made of aluminum or even plastic of some sort - and in linked segments so as not to always require a crew of riggers and a crane?

I visited a treatment plant in Indianapolis and about all they could tell us was that they were made in Germany at about a million bucks a pop and that the bottom bearings were always wearing out.