Another pump thread

whistler · #1 06/11/07, 02:19 PM

I have a gasoline powered centrifugal pump problem. I am not terribly knowledgable about pumps so bear with me.

First off, the pump seems to hold its prime. So I don't think the problem is with the intake or the foot valve.

However, I don't get any discharge when connected to a longer run. As soon as disconnect the garden hose that is 4 feet from the pump the engine buckles down and after a few sputters shoots a high volume of water with quite a bit of pressure.

Once I reconnect the 50 feet of hose I get a whole lot of nothing. Any ideas? Like I said, pumps are not my specialty so whatever you can provide will be helpful.

Whistler

moopups · #2 06/11/07, 02:33 PM

About the only thing that I can think of that applies is that your 50 foot hose is clogged with something unknown. Try blowing breath through it, if its not clogged I have no further ideas. There is no logical reason for the pump to not cause water flow.

fishhead · #3 06/11/07, 02:38 PM

A garden hose is really really small for a gasoline powered pump but it should still pump something or blow the hose connections apart. Maybe try pouring some water through the hose to check for a dead mouse or something.

fordy · #4 06/11/07, 03:27 PM

Quote:

Originally Posted by whistler

I have a gasoline powered centrifugal pump problem. I am not terribly knowledgable about pumps so bear with me.

First off, the pump seems to hold its prime. So I don't think the problem is with the intake or the foot valve.

However, I don't get any discharge when connected to a longer run. As soon as disconnect the garden hose that is 4 feet from the pump the engine buckles down and after a few sputters shoots a high volume of water with quite a bit of pressure.

Once I reconnect the 50 feet of hose I get a whole lot of nothing. Any ideas? Like I said, pumps are not my specialty so whatever you can provide will be helpful.

Whistler

...............Usually , the suction side of the pump is larger than the output side . Is it possible that the suction hose is Too small and the supply of water too the pump is insufficient ? , fordy...

agmantoo · #5 06/11/07, 05:39 PM

Discharge cavitation

Discharge cavitation occurs when the pump discharge pressure is extremely high, normally occurring in a pump that is running at less than 10% of its best efficiency point. The high discharge pressure causes the majority of the fluid to circulate inside the pump instead of being allowed to flow out the discharge. As the liquid flows around the impeller it must pass through the small clearance between the impeller and the pump cutwater at extremely high velocity. This velocity causes a vacuum to develop at the cutwater (similar to what occurs in a venturi) which turns the liquid into a vapor. A pump that has been operating under these conditions shows premature wear of the impeller vane tips and the pump cutwater. In addition, due to the high pressure conditions, premature failure of the pump's mechanical seal and bearings can be expected.

jross · #6 06/11/07, 05:42 PM

Quote:

Originally Posted by whistler

I have a gasoline powered centrifugal pump problem. I am not terribly knowledgable about pumps so bear with me.

First off, the pump seems to hold its prime. So I don't think the problem is with the intake or the foot valve.

However, I don't get any discharge when connected to a longer run. As soon as disconnect the garden hose that is 4 feet from the pump the engine buckles down and after a few sputters shoots a high volume of water with quite a bit of pressure.

Once I reconnect the 50 feet of hose I get a whole lot of nothing. Any ideas? Like I said, pumps are not my specialty so whatever you can provide will be helpful.

Whistler

Closing off the discharge of a centrifugal pump should not cause a problem so a small discharge hose shouldn't affect it except running prolonged with no flow would cause overheating and the pump would become vapor bound. It seems you may have a venting problem and your pump is getting air bound. You could tee off a small vent at the discharge side of the pump which would prevent vapor binding. Connecting a small hose from the discharge to the suction would allow recirculation and cooling. The suction hose must be at least one third larger than the discharge hose, preferably at least twice larger. To get water into a pump one must be able to get water and air out.

whistler · #7 06/12/07, 09:53 AM

Thanks everyone for responding.

More info:

The garden hose is brand new so there shouldn't be any obstructions. The intake on the pump is 2" and is placed in a lake. The outflow is also 2" but has been reduced to 5/8" at the garden hose.

Agmantoo -- without dissembling the pump is there any way to check that the problem is indeed discharge cavitation?

jross -- could I hook a two way hose splitter to the faucet head and then a garden hose to one side? that way the open side can be used as a vent to 'bleed' out the air and then closed to divert all the water into the garden hose? is there a better approach to testing/solving the problem?

Thanks again.

whistler

agmantoo · #8 06/12/07, 11:35 AM

On the output side of the pump install a large tee (cheap 2 inch pvc one) with a 1 inch or larger ball valve out one port on the tee and the hose to the other port on the tee. Start the pump with the port and the hose both open. It should now pump. Close the valve and see if it stops. If it does it is cavitating IMO. If it pumps with the valve open just return that portion of the water back to the source and use the water from the hose for your needs. This is very inefficient but should let you pump. You could make a mainfold of PVC and connect multiple (four or more) 5/8 inch hoses on the outlet

Old Vet · #9 06/12/07, 01:03 PM

A 2 inch pump will produce more water than a 5/8 hose can carry. The best thing that I can come up with is to make a manifold and hook 3 or 4 water hoses to the pump. If you reduce it more it will cavitate.

jross · #10 06/12/07, 03:26 PM

Quote:

Originally Posted by whistler

Thanks everyone for responding.

More info:

The garden hose is brand new so there shouldn't be any obstructions. The intake on the pump is 2" and is placed in a lake. The outflow is also 2" but has been reduced to 5/8" at the garden hose.

Agmantoo -- without dissembling the pump is there any way to check that the problem is indeed discharge cavitation?

jross -- could I hook a two way hose splitter to the faucet head and then a garden hose to one side? that way the open side can be used as a vent to 'bleed' out the air and then closed to divert all the water into the garden hose? is there a better approach to testing/solving the problem?

Thanks again.

whistler

A two way splitter would be the easiest way to vent the pump and you could leave a small flow through the vent to cool the pump. Also check that the shaft gland has an external or internal sealing port. If it isn't getting hot, a little water leaks out along the shaft, then it probably has an internal seal water supply. Is this a homemade setup or is it a commercially manufactured unit? I ask because it is not uncommon for folks to connect an engine or motor to a pump not realizing the pump rotates in the opposite direction as the driver. It will pump a little, but when flow is required, it cavitates and pumps nothing.

whistler · #11 06/12/07, 11:30 PM

thanks all for helping out.

i will take your suggestions and try them out. unfortunately, the pump is 200 miles away at the cabin and i won't be going until the week after next. i'll report back then and probably ask for more help.

thanks again,

whistler

ps this is a commerical setup with a homelite pump and a B&S engine.

fordy · #12 06/12/07, 11:49 PM

Quote:

Originally Posted by whistler

thanks all for helping out.

i will take your suggestions and try them out. unfortunately, the pump is 200 miles away at the cabin and i won't be going until the week after next. i'll report back then and probably ask for more help.

thanks again,

whistler

ps this is a commerical setup with a homelite pump and a B&S engine.

.............We will EXpect a Full Glass ...of a "Burbon and Branchwater" analysis after you've fully tasted er tested the Potability of the water in question . Remember , Jack Daniels kills all known "cooties" so sip with confidence whilst pumping water from your well . , fordy...

agmantoo · #13 06/13/07, 11:58 AM

The output port MUST be greater than 10 percent of the input port. A splitter will still restrict the port IMO

whistler · #14 06/25/07, 11:22 AM

thanks all for your previous help.

we did end up putting a bleeder on the line and were able to pump water through a 100' garden hose with a head of about 20 feet.

however, there was a strong surge in the outflow. we would get a good burst of water for maybe 1-2 seconds and then nothing for 1-2 seconds. the gasoline engine itself didn't surge, just the outflow.

i am guessing this is indicative of an air leak somewhere, but I can't figure out where. the pump held it's prime for 2 weeks.

any more thoughts/ideas?

thanks.

whistler

whistler · #15 06/25/07, 11:23 AM

Quote:

Originally Posted by fordy

.............We will EXpect a Full Glass ...of a "Burbon and Branchwater" analysis after you've fully tasted er tested the Potability of the water in question . Remember , Jack Daniels kills all known "cooties" so sip with confidence whilst pumping water from your well . , fordy...

just can't do it. the lake water is stained by tannin from the surrounding bogs so it already looks like Jack until you look more closely and see things swimming around.

whistler

Old Vet · #16 06/25/07, 12:14 PM

What is hapinging is that the outflow of water is too restricted. You will pump enough to make the water cavitate in spurts. Get a larger diamater hose and the problems will be solved. Go back to where the hose is reduced and get it down to 1 inch or larger then you will not have the problem. You can get a plasatic hose for it with not much money and a barb hose conetcer to hoke it up with.