Need Help with Pump Selection for Home Appliance Development

[gomachine]

I'm currently developing a home appliance and need some your help selecting a pump, so I'm posting on this forum.

The attached photos show drain pumps used in washing machines from brands like Samsung and LG. and the photo next to it is the pump connected to the housing.

1. Do these kinds of pumps have self-priming capabilities? As we all know, washing machines typically allow water to flow down to the pump by gravity.
However, the machine I'm designing doesn't have water flowing down by gravity, so I need a pump that can draw water in with some suction power.
Do these types of pumps have self-priming abilities? The second photo is a simple sketch of the situation for the appliance I'm developing.

 

[Heaviside1925]

OP,
Second sketch indicates no need for self-priming, it shows 6cm of head pressure.

 

[LittleInch]

These types of small pumps are very forgiving. Washing machine pumps run nearly dry at the end of draining.

They could probably lift ir self prime up to about 30 or 40 cm. Just buy one and experiment. They cost virtually nothing.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

The supply to the pump is below the centreline of the pump and will not "self-prime", however being an open straight bladed impeller it will act like a paddle and probably / msybe transfer a small amount of water. Look to increasing the height of you tank above the pump or make the tank deeper so the water level is higher.
If you are trying to empty the tank, forget it as it won't work.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[1503-44]

Raise the tank, or mount the pump horizontally.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Artisi]

1503, good call - horizontal mount.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[gomachine]

Thank you for your response. If we mount the pump horizontally, will it be able to self-prime? The water in question is wastewater similar to that from laundry or dishwashing, containing particles and debris that may not be fully filtered.

 

[1503-44]

Self priming is when the fluid must be pulled up by the pump to reach the pump centerline. A cheap paddle wheel pump is not going to create enough vacuum to do that.

If you mount horizontally, fluid level will roughly equal pump centerline. That will allow you to pump down to the lowest possible tank level, although you may still not get full flooding of the inlet, leaving some fluid in the tank, that will be the best you could do without elevating the tank.

To guarantee all fluid is drained from the tank, the tank must be above the top of the pump's inlet piping. To drain the pump inlet piping, the bottom of pipe pipe should theoretically be above the pump centerline. You must test the actual pump for the precise elevation conditions to know just how much you will be able to drain at partial inlet flooding. You may have varying levels of success... or failure.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[gomachine]

thank you so much. I will buy and test a few pumps out. Do you have any tips for finding pumps with self-priming capabilities? For small pumps used in appliances like washing machines and dishwashers, specifications for head and self-priming are often not well-documented. Are there any specific shapes, designs, or features that indicate a pump has at least some self-priming capability?

 

[1503-44]

I don't deal with these small things, but I would think that true self priming pumps would have tight clearences, which are needed to draw a vacuum to pull up the fluid. Tight clearence implies a certain degree of quality control in fabrication and assembly that translates into extra cost. Also higher maintenance and increased warranty costs. Not something compatible with small domestic appliances, unless you are into speciality niche products. If they are self priming, the mfgr will likely make that distinction to justify the higher price he will probably be asking for it. I doubt a paddlewheel will do it. Look for a different configuration. Not sure what would be best.

Other

Can you slope the tank bottom to drain? That may kind of convert the tank outlet into a pump inlet and keep the suction flooded longer. Highest motor speed could narrow the width of the paddlewheel for any given flow rate, reducing the pump profile. A submersible pump in a well at the tank bottom?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Compositepro]

If you have a water supply available you could use a jet pump (venturi).

 

[Strong]

Don't forget a pump discharge check valve!

Walt

 

[Compositepro]

Washing machines do not have check valves in the drain line. It will not keep water from draining back from the standpipe between loads and would be a serious maintenance problem. There is adequate volume in the pump and suction line to hold the drain-back. This water also makes the pump self-priming.

 

[Artisi]

These pumps will never be self-priming.

You could make the system "self-prine" by locating the supply tank above the pump inlet - as previously pointed out.

That's it - there is no work-around or magic, it's basic pump technology.
Even "self-priming" pumps need the case full of liquid before they will prime and pump on start, the only self-prime pumps that ewiil prime from dry are vacuum assisted - and well out of the question for this application.


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

If you want self priming and only a small head and ability to accept dirty water you could try a flexible vane pump like this

https://www.castlepumps.com/info-hub/flexible-impeller-pump-guide/

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.