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Coolant pump - how to slow flow rate?

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Grotto29/08/2021 08:29:09
146 forum posts
89 photos

Hi all,

I've just fitted a coolant pump to my lathe.
It's a small 240 volt single phase unit.

It only has an on/off switch, no speed control.

I haven’t rigged up a nozzle yet, just a hose.

when it’s on, fluid come out as fast as water from a domestic low pressure tap. I reckon it comes out faster than 2 litres a minute (spec on pump) after a few seconds I switch it off as drip tray would flood if I left it on.

Is there any easy way to slow it down?

The outlet hose is about 11mm ID - I’m unsure if I reduce if I’ll get the same volume but as a jet.

Electricty & associated stuff (resistors, capacitors, etc) is like nuclear physics to me, so unsure if a potentiometer (?) would work?

Grotto29/08/2021 08:33:34
146 forum posts
89 photos


Andrew Johnston29/08/2021 08:36:00
6283 forum posts
677 photos

Put a clamp on the hose or fit a valve in the hose.


Edited By Andrew Johnston on 29/08/2021 08:36:38

David George 129/08/2021 08:36:41
1656 forum posts
497 photos

Hi Grotto. Most coolant pumps only have a ball valve to restrict the flow and a nozzle to to direct the liquid. I always use lockline bits as they are easy to direct and the collection of nozels available are great. Just remember to check ball valve is turned off and pointing in right direction when turning on.


DC31k29/08/2021 08:50:19
578 forum posts
1 photos

Just to add to the good advice above, the pump will be a centrifugal one, so restricting or totally shutting off its flow will not damage it in any way. Just make sure any joins in the pipework are adequately clamped.

J Hancock29/08/2021 08:51:50
734 forum posts

A simple car windsceen washer set-up would probably be sufficient for your requirement ?

Grotto29/08/2021 09:11:03
146 forum posts
89 photos


I'll try putting a ball valve on it, and see if I can find my lockline look-a-like nozzle. I’ll make sure hoses are clamped.

should I be using any inline filter? I've got mesh in the drip tray sump, but not very fine.

I don’t really need a coolant pump on my lathe, but saw one with a tank which fits perfectly in my Boxford, and couldn’t resist it for $10.

Howard Lewis29/08/2021 09:18:04
5348 forum posts
13 photos

Why not rig up a by pass with a valve in it?

As the by pass valve is opened, the flow from the nozzle will decrease.

That's what is used on models locos with axle pumps and traction engines.


john fletcher 129/08/2021 09:21:41
727 forum posts

As DC 31k says, you wont be harming the pump restricting the output, but do ensure all connections are sound. Your heating system pump/circulator works just the same. Can you fix a bi-pass arrangement which puts less pressure on your connections. John

Mick Henshall29/08/2021 09:26:24
558 forum posts
34 photos

+1 for Howard's suggestion of a bypass valve


Paul Lousick29/08/2021 09:45:03
1862 forum posts
661 photos

I have a commercial coolant pump but use use one of these to control the coolant flow. Cheap on ebay and does the job. Also available with metal valves.

coolant nozzle.jpg

The tank has 2 compartments where the return coolant is drained to the 1st tank and has to flow over a wall to the 2nd where the pump is. Metal is trapped at the bottom of the 1st tank and only clean coolant flows into the second. There is also a magnet at the bottom of the 1st tank.


John P29/08/2021 09:49:44
339 forum posts
230 photos

I would have thought that the real concern here is the drainage
flow rate ,the pump you have seems to be 40 watt and 2 litres
a minute is barely sufficient as a coolant system ,most coolant
pumps are rated at about 20 litres a minute even if you don't
need it ,in any event the drainage from the tray should exceed
the maximum flow rate delivered by the pump otherwise you will
be needing a mop and bucket.


john fletcher 129/08/2021 10:23:30
727 forum posts

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

Paul Lousick29/08/2021 10:29:24
1862 forum posts
661 photos

They are not pieces of hose but specialy moulded plastic shapes that clip together. They can be bent to different anges and retain the shape.

Another option is a nozzle with a flexible metal hose. Will also require a valve to control the flow rate.

coolant nozzle 2.jpg

Edited By Paul Lousick on 29/08/2021 10:43:24

Grotto29/08/2021 10:53:49
146 forum posts
89 photos

I fitted a ball valve which slows flow. I haven’t set up a nozzle yet, but it looks like valve needs to be almost closed.

I like the sound of a by-pass. I suspect it had one as the hose from the pump had a T joint on it. I’ll refit the T and route one branch back to the tank with the ball valve on it.

Thanks Paul, I have a similar nozzle I bought years ago but never fitted. It used compressed air flow to suck coolant up a thin tube which ran through the nozzle to a brass spray jet at the end. I think I can butcher ot to make something workable.

John Fletcher - I read a post recently about someone having problems joining “hose”. It seems you need a special tool to get pieces to clip together.

John P - drainage flow rate isn’t as high as I’d like, but it will be a hassle to improve easily. Once I've fitted a by-pass I don’t think there will be an issue, but I'll make sure I keep an eye on it.

Paul Lousick29/08/2021 11:00:09
1862 forum posts
661 photos

A simple solution ifyou don't have one of the flexible hoses is to insert a piece of bendable wire inside some plastic tube to hold its shape. Cheap and nasty but will get you out of trouble .

Paul Lousick29/08/2021 11:00:41
1862 forum posts
661 photos


Edited By Paul Lousick on 29/08/2021 11:01:50

Phil P29/08/2021 11:03:07
789 forum posts
194 photos

I have two ball valves in series on my Myford, one is used to simply control the flow on / off, the other is downstream and is used to set the flow rate.

I found that with only one valve I was forever trying to get the flow rate right whenever it was moved. Also without a shut of valve the coolant drains back through the pump when it is switched off, then when you turn the pump on again you get a rush of air followed by coolant that splashes everywhere.


Edited By Phil P on 29/08/2021 11:06:13

Robert Atkinson 229/08/2021 16:00:33
1091 forum posts
20 photos

+1 For bypass back to tank. this will save energy, wear on pump and motor and noise.

HOWARDT29/08/2021 17:52:48
780 forum posts
28 photos

+1 - Fit bypass valve back to tank, restricting flow causes cavitation at the impeller.

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