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

High-Pressure Coolant System Overview

In its simplest form, a high-pressure coolant system pumps reclaimed filtered coolant at pressures up to 2500 PSIG. The required filtration level is determined by whichever component has the finest filtration requirement:

A major advantage of the Hydra-Cell Pro sealless pump design is its ability to tolerate significantly larger particulate than many competing pump technologies. While piston/plunger pumps often require filtration to 25 microns or finer, Hydra-Cell Pro pumps can tolerate particulate exceeding 400 microns. While the tooling or rotary union may still require finer filtration, utilizing a sealless pump design often enables the use of coarser filter media, reducing:

Unlike centrifugal pumps, positive displacement pumps output a fixed flow rate. Discharge pressure is created by resistance to that flow, which is often determined by the smallest tooling orifice in use. Excess flow is bypassed through a sealless pressure regulating valve (PRV) and returned to the coolant reservoir. As tooling wears or different tools are utilized, the PRV automatically bypasses additional coolant to maintain the desired pressure.

Determining Required Flow and Pressure

Proper pump selection requires knowing:

• Maximum required pressure
• Maximum required flow rate
• Pump orientation requirements

Whenever possible, consult the tooling manufacturer for recommended pressure and flow charts specific to the tooling being utilized. A generic formula for determining the flow rate required for your largest tool is:

Where:

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

This calculation can result in a table similar to the one below:

For most systems, the pump should be sized for the largest tool (requiring the highest coolant flow rate). The PRV then bypasses excess coolant when using tooling having smaller orifices. Minimizing bypassed coolant is important because excessive recirculation can contribute to:

As an example, our most common Hydra-Cell Pro coolant pump model is the D10, which produces approximately 8.8 GPM at 1800 RPM. However, many CNC high-pressure coolant applications require less than 6 GPM. For these systems we commonly utilize a 1200 RPM motor, mechanically reducing maximum output to approximately 5.75 GPM. This approach provides several advantages:

Some advanced systems incorporate variable frequency drives (VFDs) which automatically adjust pump speed based upon required pressure, minimizing bypass flow almost entirely.

Horizontal vs. Vertical Pump Configurations

Horizontal pump skids are the most common configuration and are typically installed adjacent to the coolant reservoir, often within an acoustical enclosure. These systems generally utilize:

The pump/motor adapter serves three primary functions:

• Rigid support of the pump to the motor
• Positive shaft alignment
• Coupling guard protection

Vertical pump models such as the Hydra-Cell Pro D12 and D17 models were designed to directly replace vertical multi-stage centrifugal pumps. The vertical design eliminates the need for a separate baseplate while also reducing overall component count. In many applications the system consists only of:

Vertical sealless pump designs also eliminate the dynamic seal failures commonly associated with vertical centrifugal pumps.

Important Design Considerations

Many CNC machine manufacturers offer factory-installed high-pressure coolant options, while aftermarket suppliers provide turnkey upgrade systems complete with filtration, controls, enclosures, and accessories. However, there is also significant demand for more economical systems utilizing existing filtration and coolant infrastructure.

This is where our strength lies: supplying the core high-pressure coolant system components without unnecessary added cost. When upgrading a coolant system, several important factors should be considered:

1. Verify System Pressure Ratings

Ensure all downstream components are rated for the desired operating pressure, including:

Every wetted component within the system should be suitable for the maximum system pressure.

2. Optimize Filtration

While Hydra-Cell Pro pumps tolerate relatively large particulate, other system components may require finer filtration. Determine the finest filtration requirement within the system and avoid over-filtering unnecessarily. Extremely fine filtration may increase maintenance costs, shorten filter life, and strip coolant additives, reducing coolant performance.

Bag filter housings are commonly utilized for machine tool coolant filtration and several accessories can substantially improve operating efficiency. Examples include displacement balloons which reduce coolant loss during filter bag changes, and magnetic inserts which improve removal of ferrous fines and extend filter bag life. These accessories can significantly reduce:

3. Properly Route PRV Bypass Flow

PRV bypass flow should return to the coolant reservoir in a manner which minimizes foaming and aeration. Best practices to reduce entrained air and improve coolant stability include:

• Oversized return piping
• Submerged return discharge
• Locating the return line as far as practical from the pump suction connection

4. Utilize Adequate Reservoir Volume

Ideally, the coolant reservoir volume should be at least four times the maximum pump flow rate. A properly sized reservoir improves:

Some coolant system manufacturers also incorporate baffled reservoir designs which further reduce particulate loading on filter media.

Related Articles

• Why choose Hydra-Cell Pro coolant pumps?
• Overview of a high-pressure coolant pump skid design
• Common high-pressure coolant pump applications
• Bag filter housings for coolant filtration
• Inexpensive filter bags for machine tool coolant