Sciencemadness Discussion Board

Making a highly effective aspirator recirculation pump

RogueRose - 7-4-2021 at 10:21

I was looking at either Nurdrage or NileRed's video where they were using a very common 12v pump to run a recirculating aspirator pump. I have a pump that looks the same and I have to really question if it is going to draw the vacuum that I need. I looked into upgrading the motor, but then there's the problem of the pump failing either from too high a speed/cycle rate or from seal failure from the PSI being too high. Then I thought about the cheap (or even free) electric pressure washers I see posted on craigslist. These are often the same price (used) as these 12v pumps that are sold on ebay and just about any of them will provide more than what would be needed to run an aspirator pump.

You can also find just the pump head's on ebay for really good prices (I found a working 3200PSI 2.8GPM used unit for $22 shipped) and all you need to do is connect a motor or engine to it. I've taken a number of these apart and they use brushed universal motors that are probably pretty high RPM, I'm guessing 7200-12,000 and are rated from .75-`1.5HP - depending on the size unit you have. But the easiest thing would be to find a used working electric unit.

All you would need to do is find some kind of restriction valve that will get the water to the pressure/velocity that you want (which will be much lower than what would be coming out of the wand), make a T fitting and install the aspirator right where the water exits the restriction orifice and you will have a high pressure/high volume aspirator pump that can recirculate water.

My biggest question is what kind of restriction orifice/valve should be used, b/c it would be really nice to be able to change it to tune it for different applications. I'm thinking some kind of a needle valve might work or even a normal ball valve followed by a restriction orifice (like a cone with a hole drilled out of the middle).

If anyone more experienced with plumping and hydraulics can think of a reason this wouldn't work, I'd like to hear your thoughts - or if there is a different method, I'm open to that as well. I think something like the lowest powered, 800psi, 1.2-1.6GPM unit might be more than sufficient. I'm also thinking that one of those router speed controllers will work great for this as I use them to control universal motors all the time, so if you have a unit that is too powerful, you can just slow it down with this $15 device (the $3 ebay units may work as well!) and still be able to use it at higher pressures should the need ever arise.

wg48temp9 - 9-4-2021 at 10:34

I have repaired and/or dismantled several high pressure washers. They all had inductions motors in them. They had a pressure switch in them that cuts the power to the motor when the trigger is released on the wand. At least one had a by pass valve on the pump probably to stop pressure build up as the motor runs down.

If what you are suggesting is to reduce the output flow by partially closing a valve in the output, that could trip the pressure switch or by pass valve. If your pump has a universal motor it would be better to control the power to the motor to reduce its speed and hence pump flow. Not so easy with an induction motor.

monolithic - 9-4-2021 at 11:35

Most aspirators need 6-8 liters/minute flow rate and tap pressure is like 40-60 psi. Can you realistically get that out of the pump heads? I'm not sure. Pressure washer pumps are reciprocating, so you might get pressure fluctuations inside the venturi which may screw up the vacuum. Most commercial lab aspirators use a centrifugal pump for this reason. Just food for thought, since I know a lot of people had issues with recreating NurdRage's recirculating pump, and complained of little/no vacuum.

wg48temp9 - 9-4-2021 at 22:20

Quote: Originally posted by monolithic  
Most aspirators need 6-8 liters/minute flow rate and tap pressure is like 40-60 psi. Can you realistically get that out of the pump heads? I'm not sure. Pressure washer pumps are reciprocating, so you might get pressure fluctuations inside the venturi which may screw up the vacuum. Most commercial lab aspirators use a centrifugal pump for this reason. Just food for thought, since I know a lot of people had issues with recreating NurdRage's recirculating pump, and complained of little/no vacuum.


Yes I think your correct about the flow rate of cheap electric pressure washers. They range from 3.5l/minute and up to about 6l (spec limit at TOOLSTATION, probably optimistic) for bigger and expensive ones.

The washers I have examined had three pumping cylinders operating in parallel and 120deg out of phase with each other so there is always at least one cylinder supplying water. So the flow will never drop to zero but it will still have some ripple in the flow rate possibly smoothed by the inertia of the flow and the elasticity of the pipe feeding the wand

Below is an explanatory diagram of how a 3 phase half wave rectifier works
.

Fyndium - 10-4-2021 at 00:45

The pressure provided by powerjets is somewhat pulsed, but the pulse cycles cross each other so the pressure fluctuation is constant and marginal, and this would likely not trouble the vacuum. In case of bigger swings like changes to pump rpm, it would have an effect.

Running an aspirator with 220bar pressure would be.. interesting. In a positive way. You would need a metallic aspirator and hydraulic couplings though, it will blow up any other parts apart instantly.

I have a centrifugal garden pump that delivers 4bars of pressure, I haven't tested it with aspirator, but the thing is pretty damn noisy and it is also way too large, it can supply something like 5000 liters per hour so it would run at less than 10% efficiency at best.

The NurdRage pump system wonders me too. I got that exact same pump, and I was not able to get it to produce any reasonable vacuum, and it is also hefty noisy, much more than my rotary vane pump. I ended up getting a small chinese diaphragm pump for suction filtrations and it works great.

RogueRose - 10-4-2021 at 18:27

Quote: Originally posted by wg48temp9  
I have repaired and/or dismantled several high pressure washers. They all had inductions motors in them. They had a pressure switch in them that cuts the power to the motor when the trigger is released on the wand. At least one had a by pass valve on the pump probably to stop pressure build up as the motor runs down.

If what you are suggesting is to reduce the output flow by partially closing a valve in the output, that could trip the pressure switch or by pass valve. If your pump has a universal motor it would be better to control the power to the motor to reduce its speed and hence pump flow. Not so easy with an induction motor.


I was playing with a pressure washer not long ago and when I removed the spray tip (removed it from the wand) and pulled the handle trigger, the water sprayed out about 40-60+ft in a beautivul laminar flow of higher pressure than what is possible from our tap, but at lower volume. The pressure washer was rated at 4.8GPM at 3600PSI and I'm guessing the volume was higher than 4.8GPM here, though I could be wrong.

My thought is to create a new tip/nozzle, instead of one that is so restricted, create a much larger opening (ideally with laminar flow) and that is adjustable. The aspirator would connect basically at the same point, just in front of the opening.

While looking for pumps and doing some cleaning up, I came across a large box of old oil and water pumps from cars fro 1950 - 2000. They are ALL pulley driven and I suspect these would be ideal for creating a pump for this, as they are meant for circulation and at varrying presures and speeds - well within the ranges we are looking for. All of them could be affixed to a piece of sheet metal and mounted with bolts going through. A pulley could be printed from a 3D printer, purchased or there are lots of other options.

I personally need a few pumps to circulate very hot heated oil as well as cold refrigerant and I think I've finally found the proper pumps that will be affordable (ebay I found used pumps for $10-50 - some looking brand new and all in working order - junk yards are also places to find these at good prices). Findig a pump capable of 300-500+ degree oil, I was looking at $400-1000+ for a unit that could handle this - but as usual, finding already existing products for mass applications always provides an affordable solution!

I'll get the motors out that I removed from old pressure washers and show you what I've found. They seem kind of similar to vacuum cleaner motors except they are longer rather than wider like vacuum cleaners, and they might run at slower speeds than vacuum cleaners.