Water cooling pump - suck vs. push

Dear Forum,

Just making up my mind about a water cooled spindle.
When thinking about risks / possible fails I came also to leaking water hoses and connectors.
Pushing the coolant into the system will spill all of coolant somewhere until the reservoir is empty.
Sucking it through the system will pull air into the hoses but probably no or little coolant will be spilled.

So, sucking seems to be the better option to me.
Any opinions on that.


My set up is a push system I have a submersible pump in my coolant tank.
The coolant keeps the pump cool and does a lot to deaden the noise of it, it intakes via a mesh grill in the pump body and discharges through the coolant pipe via a flow indicator mounted near to the Onefinity screen, then to the spindle return pipe follows same route back to tank with no flow indicator and discharges via a pipe that is secured into the tank below the surface level of the coolant.
I use a mix of deionised water and high quality vehicle coolant that colours the liquid. Flows and pressures are all fairly low, I have no issues with spindle/coolant temp and no leaks yet.
I did use high quality pipe and fittings and always inspect them at the same time that I do a clean and oil on the Onefinity


Hey Andreas,

I wouldn’t take any hose connections at all where I have to worry about something like that. As far as I’ve heard, there are problems only with the hose connectors on those cheap Chinese spindles or people clamping their spindle to death in the spindle mount until the spindle housing cracks and the water leaks out.

My spindle has the Festo QS8 tool-less hose connectors and Festo hoses, so I sleep easy.

I have no experience with the no-spill quick disconnect fittings Daniel @PwnCNC offers, maybe someone has?

The pump will pump liquid into the hose as long as there is liquid in the tank.

If you have a cooling station with flow sensor and the flow collapses, it can send the VFD an alarm signal which will stop the spindle (and the g-code program if wired to CNC controller correctly)


Push. Most of the small pond type pumps aren’t high efficiency pumps. They are designed to sit in the reservoir. they count on both atmospheric pressure and the weight of the water above the pump inlet to push water into the pump. If sucking you will need to prime the pump and even then it could cavitate or possibly collapse a vinyl hose cutting off flow. Pushing water is almost always the easier way.


I would opt to push based on prior experience, less priming issues. If you’re doing a closed loop system then you could go either way…

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Dear All,

Thank you so much for all of your answers - that was really helpful.
Special thanks for pointing me to FESTO connectors and cooling stations.
Doing a little bit of searching and mathematics, I found a cooling station for under EURO 200,- with flow and temperature alarm.
BTW: While searching through all of this material, I found that purified water is the best coolant when freezing and corosing protection is not needed. (OK - no colored liquid in the pipes…)


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I have a 80 mm 1.5 kw water cooled spindle. Anyone know what operating temperature range is?

Hey Sean,

in my spindle datasheet, it says “max. 35 °C”. I own a 2.2 kW 80 mm water-cooled spindle.

In my spindle manual, the manufacturer recommends in its Safety Warnings …

automatic monitoring and automatic disconnecting power if the coolant flow rate falls below 1 liter/min, or the temperature after the motor spindle exits motor spindle exceeds 40 °C.

My cooling station has sensors for this, and triggers alarms when that occurs, through a three-pin circular connector which I can connect to the VFD, the system’s Safety relay, or to the CNC controller.

Furthermore, my spindle manual says:

Water-cooled motor spindles:

When dimensioning the cooling system, it must be ensured that the temperature of the cooling liquid leaving the motor spindle does not exceed the permissible value of 30 °C in normal operation.

At least one flow indicator and one temperature sensor with temperature display must be installed in the cooling circuit so that they can be easily seen by the operator and used to monitor the cooling system. Temperature monitoring must take place after the motor spindle has left and before it enters the heat exchanger. If the cooling system is monitored manually, check every 15 minutes during operation whether the coolant is within the permissible temperature range and whether there is coolant circulation. If the coolant does not circulate, or if the temperature exceeds the permissible limit, stop operation immediately and correct the problem.

Use special coolant that ensures corrosion protection of non-ferrous metals, does not attack rubber seals and has the lowest possible electrical conductivity. Use only coolant offered by the manufacturer.

My spindle is this, my water chiller is this. My coolant liquid is this.

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Thanks for the info. I used computer cooling components to create a closed loop system using a flow gauge just before the input input on the spindle to see the system running. I use Koolance 702 Liquid Coolant, High-Performance, UV Blue. I have a radiator with CPU fans and an inline pump with a digital temp readout. The majority of the time it runs at ambient temp which have been about 95f / 35c during the summer heat in my non-climate controlled garage. I have had a few longer and intensive carves get up to 105f / 40.5c.
Everything seems to be working well but I am thinking of adding some type of active cooling to the line to better regulate the temp. I like the idea of having the temp sensor connected to the VFD or better yet the Masso controller. Next project!

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Hey Sean,

In any case, a running spindle must not be disconnected any other way than by the RUN/STOP command of the VFD, and never by a switch, otherwise spindle or VFD could take harm.

If it has to be simple, I would connect the cooling station’s sensor outputs to VFD input terminals. The temp or flow sensor connected to an input terminal of the VFD can trigger immediate spindle STOP (if terminal is assigned to the corresponding function).

The VFD would then also be able to trigger stopping the running program on the CNC controller.

Image: KG5000+ Cooling station (back)
Left: Festo QS8 toolless hose connector, right: circular connector for temperature and flow rate alarm

Of course the system’s Safety relay circuit (e.g. Omron G9SE) or the CNC controller are also able to send RUN/STOP to the VFD if wired correctly.

To dimensionate the cooling system it’s the flow rate of the pump and the amount of coolant liquid (tank size) that matters. Expensive cooling stations have also bigger cooling windings and a bigger fan, here is one forum member that opened their device: Anyone using the Vevor CW3000 water chiller for their water cooled spindle?

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