How to Properly Size a High-Pressure CNC Coolant Pump System

High-pressure coolant on a CNC machine clears chips, stretches tool life, holds tolerance and improves finish. A lot of systems still fall short on pressure, flow or uptime.

Piston, plunger and multi-stage centrifugal coolant pumps use dynamic seals. Those seals wear, leak coolant and stop the machine. A Hydra-Cell^® Pro is sealless positive displacement — no packing in the coolant — and it will pass coarser solids than those designs, so filtration can often be opened up.

What follows is the information needed to size the high-pressure end of a CNC coolant system.

High-Pressure Coolant System Overview

In simple form the system takes filtered, reclaimed coolant and delivers it at up to 2,500 PSIG. Filtration fineness is set by the tightest part in the loop:

• tooling
• rotary unions
• valves
• the pump

A Hydra-Cell Pro will live with particles larger than 400 microns. A piston or plunger pump often wants 25 micron or finer. Tooling or the rotary union may still need the fine bag; the pump itself usually does not. Coarser media means fewer bags, less coolant dumped at change-out, and fewer stops.

Unlike a centrifugal, a positive-displacement pump puts out a fixed flow. Pressure comes from resistance — usually the smallest tool orifice in use. Extra flow goes through a sealless pressure regulating valve (PRV) back to the tank. As tools wear or change, the PRV bypasses more or less to hold set pressure.

Determining Required Flow and Pressure

You need:

• maximum pressure
• maximum flow
• horizontal or vertical pump

Use the tool maker’s pressure and flow charts when you have them. A generic orifice equation for the largest tool is:

Where:

• Q = coolant flow
• C_d = discharge coefficient (typically 0.65–0.80)
• A = total orifice area
• ∆P = coolant pressure
• ρ = coolant density

That math produces a table like this:

Orifice Diameter (in)	Orifice Diameter (mm)	Flow at 100 PSI (GPM)	Flow at 300 PSI (GPM)	Flow at 1,000 PSI (GPM)
0.020"	0.50 mm	0.2	0.3	0.6
0.030"	0.75 mm	0.4	0.7	1.3
0.040"	1.00 mm	0.8	1.4	2.5
0.060"	1.50 mm	1.8	3.2	5.8
0.090"	2.30 mm	4.0	7.0	13.0
0.125"	3.18 mm	7.8	13.5	24.5

Size the pump for the largest tool. The PRV dumps the extra when smaller orifices are in the spindle. Keep bypass down. Too much recirculation heats the tank, pulls in air, foams and wastes power.

The D10 is the coolant frame we sell most. At 1,800 RPM it makes about 8.8 GPM. A lot of through-tool work wants less than 6 GPM. A 1,200 RPM motor cuts that to about 5.75 GPM and you get less bypass, a cooler tank, less foam, a quieter skid and better efficiency.

Some systems put a VFD on the motor and trim speed to pressure so almost nothing goes over the PRV.

Horizontal vs. Vertical Pump Configurations

Most skids are horizontal, next to the tank, often in an acoustic box. Typical pieces:

• steel baseplate
• motor
• shaft coupling
• pump/motor adapter
• pressure regulating valve

The adapter holds the pump to the motor, keeps the shafts in line and covers the coupling.

Vertical Hydra-Cell Pro D12 and D17 frames were built to drop in for vertical multi-stage centrifugals. No separate base. In many jobs the package is pump, motor and coupling. The sealless wet end also removes the packing failures common on those vertical centrifugals.

Important Design Considerations

OEM high-pressure options and turnkey aftermarket packages include filtration, controls and enclosures. Plenty of shops only want the high-pressure pump on filtration they already own. That is the core we supply. When you add pressure to an existing tank, check the following.

1. Verify system pressure ratings

Everything downstream has to be good for the set pressure:

• hoses and fittings
• rotary unions
• valves and manifolds
• filter housings

Every wetted part should match the maximum system pressure.

2. Optimize filtration

The pump will take large particles. Other parts may not. Filter to the finest requirement in the loop — not finer. Extra-fine bags cost more, load faster and can strip additives out of the coolant.

Bag housings are the usual coolant filter. Displacement balloons cut coolant loss at bag change. Magnetic inserts pull ferrous fines and stretch bag life. Both cut coolant buy-back, bag use, disposal and downtime.

3. Route PRV bypass correctly

Bypass should re-enter the tank without beating air into the coolant:

• oversized return piping
• submerged discharge
• return as far from the pump suction as the tank allows

4. Use enough reservoir volume

Aim for tank volume at least four times maximum pump flow. That helps solids settle, air leave, heat leave and the mix stay stable. Baffled tanks cut the load on the bags further.

A Hydra-Cell Pro sealless coolant pump replaces packed high-pressure designs, opens filtration and ends dynamic-seal leaks on the pump.

Related Articles

• Why choose Hydra-Cell Pro coolant pumps
• High-pressure coolant pump skid design
• Common high-pressure coolant pump applications
• Bag filter housings for coolant filtration
• Filter bags for machine-tool coolant
• High-pressure CNC coolant skid design
• Sealless pressure regulating valves