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Coolant pump - how to slow flow rate?

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Andrew Johnston29/08/2021 20:04:24
6316 forum posts
677 photos

Interesting; most of my coolant pumps, 3-phase industrial and single phase home brew, simply have a tap on the output to regulate flow. Ironically the only pump that failed (motor winding short) was the 3-phase OEM pump on the Bridgeport, which didn't have an output tap.


duncan webster29/08/2021 20:16:02
3588 forum posts
66 photos

Industrial centrifugal pumps are regulated by bypass, either back to tank or of not convenient, back to inlet. More modern method is VFD, but that would be overkill for a coolant pump.

Chris Crew30/08/2021 02:01:00
150 forum posts

You won't go wrong with a coolant pump IMO. Any finish or parting-off problems will be reduced at a stroke. The only issue is that sometimes things can get a bit messy, especially when working near the chuck and the flow of coolant hits the jaws but the other advantages of a continuous flow more than compensate for this, again IMO. I use the cheapest soluble oil from the local oil merchant diluted 20:1 and mix the water with the oil rather than the oil with water. I also put in a good squirt of the Rocol anti-bacterial potion when I replenish the reservoirs as I had issues with black gunge when the machines had not been used for a while. It appears also that the Rocol lessens the tendency for the water and oil to de-emulsify over time, although that might just be my perception.

I accept that some people are very wary of having anything containing water anywhere near their cherished machines but I have always used copious amounts of water soluble coolant since I was an apprentice and we were always instructed to swill down the machines with coolant after use. You will find that a film of the oil will reside on the exposed metal surfaces and will guard against rust but you may experience some staining between mating surfaces over time, such as under tool-posts etc.

Chris Mate30/08/2021 06:56:24
26 forum posts
3 photos

I am busy installing a Mill/drill 7045M which came with a swivel bed and coolant pump and tank no choice, facing the same problem. Going to use extra valve to run output back to tank, just exactly how I am going to do it, I am thinking about on how to aerate that streem as well back in tank. I also going to install a smaller catch tank within the tank to keep oily impurities to a smaller surface, and that has an overfow to a small tank as it rises, thats the plan for now.
Maybe add airpump drawing minimal power as well.

JasonB30/08/2021 07:36:55
21630 forum posts
2493 photos
1 articles
Posted by john fletcher 1 on 29/08/2021 10:23:30:

I have several short pieces of BLUE hose as shown in Paul Lousick comments above. Can any one tell me how to join them up, I have tried hot water and hot air gun. Not there yet but keep on trying. John

The small sizes I just snap together by hand. 


Edited By JasonB on 30/08/2021 07:40:01

Grotto30/08/2021 08:30:02
148 forum posts
89 photos

Thanks for all the advice.

I've fitted a by-pass. I put a tap on it, but it wasn’t necessary and didn’t seem to add anything so I took it off.

I was running the by-pass into a T joint with the sump hose, but the sump was draining slowly, so I've separated them, and the sump drains fine, even on full flow.

Nozzle is work in progress.

Here in Auckland, we're in lockdown, so no chance to buy anything. I'm having to make do with what I've got and spends a few hours making stuff you can normally buy down the road for a few dollars, but I’m not getting bored.

Trevor Drabble30/08/2021 09:08:22
265 forum posts
5 photos

Grotto , Assuming you're using a water-based soluble oil solution , my suggestion would be to simply switch to using cutting oil instead . As well as other benefits , the greater density slows the flow rate considerably. Trevor.

noel shelley30/08/2021 10:29:46
855 forum posts
19 photos

WHY would you want to aerate the return flow to the tank ? I would expect this to increase the risk of microbial action. To reduce the risk of frothing or aeration in the tank on the return, take the return pipe down below the lowest level of the liquid in the tank, ie a dip tube. Good luck Noel.

bernard towers30/08/2021 11:20:58
337 forum posts
89 photos

Always told by the Texaco oil rep to stir the water vigorously and drip the necessary amount of oil into the water, he said only way to guarantee total mixing.

Mike Poole30/08/2021 12:42:00
3095 forum posts
72 photos

Coolant pumps are usually primitive affairs that are not in any danger of developing any serious pressure, they seem quite happy to have the output completely blocked and looking at the clearances the impeller has to the pump body then it will just thrash round doing not very much. The flow control tap on my coolant delivery goes from completely shut off to full flow and anywhere in between. If you don’t require any flow for an extended period then just turn the pump off. I tend to just push the delivery nozzle out of the way if I want to inspect or measure the job which saves having to reset the flow and it’s easy to just swing the nozzle back to where it was..


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