Looking for a Compact Positive Displacement Pump

less than $20? boy, you weren't kidding when you mean you dont need precision. I have some flow meters that cost in the $1500-$2000 range that are still not precise enough for aerospace. output? 4-20?, 0-5?, digital?

For the pump, i would have to say a small gear pump seems a good match for your application due to size. (i assume this without knowing many factors, such as fluid viscosity, contamination etc)

What type of volume (qty) are you talking about? I work for a fluid power distributor, and can provide some contact information or application help if you like. And maybe we can even provide a quote.

In your post you stated 15 gpm twice. The Procon pump you cited is rated for 15 to 140 gph; not gpm. I'm guessing 15 gph is what you want.

The package size of the Procon likely has a lot to do with the motor size, which in turn is driven by both the pressure and flow it's designed for, both a lot more than you need. Since you are at the low end of the flow rating you ought to take a look at whether you can drop the pressure and put your selection into a much smaller pump with a smaller frame fractional motor. I don't know much about the Procon products; but from the description of their applications I'd guess they offer smaller pumps than the one you've looked at.

Ed Weldon

You're correct - I meant 15gph. It is the size of the pump with motor that is my highest priority. Procon, Fluidotech, and a number of other offer pretty comparable lines of these pumps destined for beverage dispensing/carbonating, welding coolers, circulators, espresso machines, etc. The 'canned motor pump' CMP-7000 from Procon is the most compact way of delivering 15gph at at least 45psi that I have discovered so far among positive displacement pumps. I have apparently stumbled into an unmarketable niche that would require custom design. I cannot afford that.

Even if that procon pump body came separate I'd be able to source my own motors to fit, but alas, it's integral to the motor (the support bearing). Fluidotech has a similarly compact model, that is many times more expensive, and is 'canned' as well and not available as separate pump body. All of the other pump bodies in their lines, when affixed to motors, add 3 to 4 inches to the pump length.

It's frustrating that I cannot find a source of miniature vane or gear pumps, similar in size to the MicroPump models, that are priced economically enough to put in a consumer product.

look at electric automotive fuel pumps.

Thank you for that. I have googled just about every iteration conceivable for these pump styles and fuel pumps have come up before. They are indeed often (always?) vane style pumps and available in a very wide range of delivery/psi. There are versions for those twin engined off-shore cigarette boats that will deliver gas like your kitchen faucet! Yikes! Those guys gotta be rich.

But common (ie affordable) electric fuel pumps are duty not rated for constant circulation at 15gph. They are, more critically, not manufactured of wetted parts suitable for water. They'd corrode eventually. Also, when you do get up in the flow ranges I'm looking at, they are, from what I've read on other forums, pretty damn noisy. In the racing environment they were designed for, engineers had the luxury of not being concerned with making noise). The marine versions certainly must be made for water, even salt water. But that is no gaurantee that internally they are as well. The manufacturer never really had to design for coolant/water.

Finally, to get to that level of performance and suitability in an automotive pump, it would come in at about 500 to 1000 USD. I'm right back where I started and may as well just purchase the exquisitely suited MicroPump annular gear lab-pump for that price.

I just know that the holy grail (for me) is out there somewhere. I just have to eventually find the guy who sells it. Something like this...

http://www.coleparmer.com/Catalog/product_view.asp?sku=0701220

...but with just a bit more oomph! This is at the upper limit at affordable PD gear/vane pumps for this type of service, and at a reasonable price. Then you have to jump clear up to the Procon/Fluidotech pumps that are many many times larger and more powerful. There's a pretty big gap there with nothing filling the market.

Geb --

I fear you are fighting a losing battle here. Your nemesis is the 45psi in your system design. Your liquid is water. The first thing the positive displacement pump people will tell you is that rotary pumps (gear, vane, etc.) don't do well pumping water at high pressures. What they are really saying although the sales guys don't like to admit it is that type of pump wears out and loses pumping efficiency. They seldom have any data on how long that will take. Applications vary too much.

The best performance of these pumps come from having precise minimum clearances in the pumping elements and their bearing surfaces. Unmachined molded parts do not do well. And water is a poor lubricant for bearings. Under $100 price with a motor does not leave much room for precision machined parts in the pumping end of the unit.

Can you use a small piston pump? This may be a better choice; but I fear the inherent vibration or continuous duty may be its undoing. Such a pump will not do well unless the liquid is free of solid matter.

As I mentioned before you really need to revisit that 45 psi pressure requirement. Is this a real system requirement such as the need to feed a nozzle or a very small cooling passageway? Or is it a consequence of an engineering decision to use smaller size tubing and fittings to save money, weight or space in the system design?

Ed Weldon

Ed thank you so much for the input. This app is for tig torch cooling. The pump needs to be volumetric/PD in order to present a calculable flow rate (usually about 15gph) to a range of hoses and torches which may vary slightly +/- 1/8inch id supply line running from 24 to 50 feet and through a torch head with varying amounts of restriction depending upon manufacture. This is, in normal circumstance, achievable with about 20psi.

Welding cooler manufacturers rate their pumps at three to four times this, and up to 360gph. This is in order to accomodate the possibilty of multiple users, or use of the machine with other welding processes that require higher capacity cooling, including water cooled plasma cutting, and industrial automation.

I'm only interested in mid range tig welding machines dedicated to a single user. That puts me pretty reliably at 15-20gph needing no more than about 45psi for good margin. Every tig cooler available uses a vane or gear pump, with generally reliable results... 24/7 in some shops at up to 18months servicelife. I'd just like to find one that fits this niche without such overkill for the individual user (and wasted space/weight in my design).

If there were another commonly available style of pump, liquid ring, diaphram, oscillating piston (vibe pump), whatever, that could measure up to this in price and performance, I'd be perfectly willing to buck the trend in welding coolers and work with it. I just don't see it so far in any of my research. Hope someone here can point me in another direction.

Geb --You seem to be looking for an off the shelf pump-motor combination to do this job. Your desire for a compact package suggests the mechanical efficiency (in the 75% range) of a gear or vane pump (they are pretty good that way before they wear out their close clearances) in order to get the advantages of a physically small motor. You are therefore somewhat locked into what you have found so far, which at this point, doesn't look that great.

If you are able to go outside the box and do some pump development work take a look at using a centrifugal or regenerative turbine type pump driven by a universal (brush type) motor. The beauty of universal motors is that they are not constrained by the rotational limits of 2 pole AC induction motors (3600 rpm). Another nice characteristic of universal motors is that they are smaller for the same power output than an induction motor. Witness the broad use of this motor type in power tools.

Note here that the pressure produced by a centrifugal or regenerative turbine pump (Whirlpool used these in the ill-fated Calypso washing mashines) goes up by the square of the rpm's; i.e., double the rpm's, 4x the pressure (and 2x the flow). But flow on centrifugal pumps can be throttled; unlike positive displacement pumps that can only have flow limited by bypass valves like you have in automotive oil pumps.

Efficiency of centrifugal pumps in this size range will be on the order of 40-50% (less when throttled back from their maximum efficiency point) At 7000 rpm it may be necessary to pressurize the entire system to prevent the pump from cavitating at the inlet. Also you will likely have to allow for a maintenance cycle of a few hundred hours to replace motor brushes. And lastly, your enterprise will need to have the resources to support some pump development effort assuming the market potential for a product is big enough to payback.

There are texts on the subject of centrifugal pump design and knowledgeable consultant engineers (one posts here on CR4) available to provide technical information.

Ed Weldon

RVZ717, precision is not that important for this application. I merely would like to have the flow rate displayed on the panel so that it could be adjusted via bypass to approx 15gph +/- 10percent or so.