Rapid change of turning a motor on and off (+ water pumps)

Thread Starter

Paán

Joined Nov 9, 2016
1
Hello forum, a bit of an urgent situation here.

I have this installation with a water pump, that should work for at least 2 months, in a way that it gets electricity for 8 seconds than its off for another 8 seconds. After a while it starts to exhaust somehow, the pump is not pushing enough water up, which results in major problems.
I think it has something to do with the engine inside wasn't designed for such use. It's a Barwig 12V waterpump, 18L/min.
I bought in the meantime anther pump that is mechanical, it was ment to be used with a drill. You hook the drill onto the propeller of the pump so the drill can make the pump go. I'm planing to buy an engine that runs this pump and is good with the rapid change of use work,
but this is as far as i got with my skills of solving problems not supported by an electric background knowledge.
I would ask if the forum thinks thinks if I see the problem right and if so, what type of motor or other solution would you recommand?

Thanks
Pán
 

drc_567

Joined Dec 29, 2008
772
Just from the physical properties involved, water pumps are deficient on the suction, or intake side. If the intake loses continuity of flow for even a moment, the output flow could be terminated. ... Suggest getting as large a diameter as practical tube or hose for the suction intake tube, and by some means ... duct tape or something ... splicing that onto the pump intake. Doing this will reduce the dynamic/friction head loss on the intake of the pump.
 
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MrSoftware

Joined Oct 29, 2013
1,674
Other than finding a motor built to take that type of duty cycle, I don't have any motor tips. But, is there a reason you cannot use a reservoir to hold the fluid under pressure, so your pump duty cycles can be longer, and use a valve to turn the flow on/off in 8 second intervals? The reservoir can either be a tall tank, using gravity to maintain pressure, or it can be a tank with a water bladder and space for air, where pressurized air maintains the water pressure.

OR, set your pump up to run continuously and use an electric valve to control a bypass on the output. Either dump (vent) the extra water, or recirculate it back to the intake side of the pump. Now your pump duty cycle is 100% and the valve controls the flow. I'm thinking this will be easier on your pump motor than constantly restarting.
 

MaxHeadRoom

Joined Jul 18, 2013
19,968
It is not stated whether what style of pump and the application, is it a submersible, or a lift pump or?
What is the rate required?
According to the manuf. site, these are just small sump pumps.
Max.
 

drc_567

Joined Dec 29, 2008
772
^ The post above by MrSoftware, suggested the best option ... recirculation. If you construct a small 'reservoir' at the suction intake, and use a small diameter tube attached to the pump output downstream to keep that reservoir filled, you should be able to maintain the pump 'prime' even during the 8 second period when it is turned off. Just use a length of larger tube and a tee fitting to build the intake container. .. no problem.
 
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drc_567

Joined Dec 29, 2008
772
... as far as building practical working device according to the OP's requirements, how much of the
0.3 L/sec output flow rate could be spared to recirculate to the input reservoir?
 

MaxHeadRoom

Joined Jul 18, 2013
19,968
If it is used as intended as a submersible pump, there should be no problem with priming. Assuming the pump is permanently submerged.
Max.
 

tcmtech

Joined Nov 4, 2013
2,868
Us knowing the full details of the system and its intended use would be greatly helpful.

Where are you pumping water from?
Where does it go?
How much needs to be moved in any given time frame?
What power source are you using?
What made you decide to do things as you did?
 

drc_567

Joined Dec 29, 2008
772
The specification sheet for the Barwig pump shows a maximum cable length of 1 meter. That sounds like a very short distance to plug in the pump.
 

MaxHeadRoom

Joined Jul 18, 2013
19,968
These pumps appear to be intended for boats and campers etc, I would hesitate to use this pump for a industrial use, or continuous/intermittent operation for heavier use than intended.
Max.
 

MrSoftware

Joined Oct 29, 2013
1,674
My impression from the OP message was not that he was loosing prime, but that the motor was losing output capacity (getting weaker) after many on/off cycles. As in the motor itself is failing.
 

Reloadron

Joined Jan 15, 2015
5,100
I think you need to gain an understanding of "head and flow" and answer the questions posed by members. You really have not defined your application. If you want to push a column of water up you need to define how high? You may want to give this a read:
CENTRIFUGAL PUMP SYSTEM TUTORIAL
 
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