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Basic Pumping Principles 102 - Give Your Gear Pump Some Room

rotary lobe pumps
by Eric Lunsford
May 5, 2014

Basic Pumping Principles 102 - Give Your Gear Pump Some RoomBasic Pumping Principles 102

Last spring I was visiting with one of our customers in Middle Georgia.

They were having two problems with an application involving a Viking L4724 Positive Displacement Internal Gear pump. Basically the pump was being used to recirculate their material in a large storage tank. However, they also used it to introduce some additional material by adjusting some valves in their pipework.

The first issue was a loud racket being made by the pump when they started it up to add material to their process.

The second issue was the amount of time it was taking to pump down a 55 Gallon drum which is where the material comes from that they want to add to the recirculation tank.

When I approached their process with their engineer I asked him if it was ok if I stated the obvious, to which he replied “sure.”

The first thing I pointed out was the distance between the pump suction port and the Tee/Valve where they change the intake material was nowhere near long enough. Basic Pumping Principles 102, you need a straight run of pipe 10 times your pipe diameter to allow for proper friction loss before your liquid enters your pump. This was causing the pump to cavitate which was causing the racket they were hearing upon pump start up.

The next thing I pointed out was that they were using a 1” steel pipe connected to about 8 feet of 1-1/2” hose connected to their 2” Tee, located about 6” from their pump inlet, in order to pull the liquid out of a 55 gallon drum. Can you say starvation AND cavitation?

I spoke to their engineer and he agreed that these issues were a problem but they couldn’t be fixed and he wanted me to solve the two problems as best I could based on these conditions.

He felt that putting a VFD (variable frequency drive) on the motor of the pump would allow them to start it ‘softer’ and ramp up allowing material to get to the pump before it hit full speed and he figured that should stop the racket and possibly drain the 55 gallon drum a little bit quicker.

Well, the customer is always right. I told him that I didn’t think a VFD would solve his problems but if that’s what he wanted then that’s what we would quote him.

The moral of the story is, know your pumping basics BEFORE you build your pump system. A good foundation in pumping principles would have done wonders for their process and would have negated these issues from the beginning.

Don’t make this mistake yourself. If you have questions, call us. That’s what we are here for.

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