Flow monitoring in cooling systems and machine lubrication: why a pressure gauge is not enough
Flow monitoring in cooling systems and machine lubrication is one of the most direct applications of a ChemTec flow monitor in the manufacturing industry. A CNC cooling system flow monitor, also known as a coolant flow monitor or coolant flow switch, detects not only whether the pump is running but also whether the coolant actually reaches the spindle, the tool or the lubrication point. That distinction makes the difference between a machine that stops when a nozzle is blocked and a machine that keeps running until the tool breaks.
⏱ approx. 6 minutes reading time
Measuring pressure is not the same as monitoring flow
In the coolant and lubrication systems of CNC machines, machining centres and industrial equipment, a pressure gauge is routinely installed to monitor the system pressure. That gives a false sense of security: pressure being present does not prove that the liquid is flowing. A pressure gauge does not detect a blocked coolant nozzle, because the pressure in the main line remains normal as long as the pump is running. Only a flow monitor in the coolant line detects that nothing is reaching the cutting point any more.
A blocked nozzle, a partially closed valve, a defective pump that builds up pressure but delivers no flow, or a leak further down the line causing coolant to leak past the machine instead of reaching the cutting point: all these situations give a normal pressure reading while the critical points are running dry. A flow monitor in the coolant or lubrication line, referred to as a coolant flow monitor or coolant flow switch CNC, detects each of these situations immediately.
Pressure gauge
✓ Pressure present in the line
✗ Whether the liquid is actually flowing
✗ Blocked nozzle or distributor
✗ Leak further down the line
✗ Pump that builds pressure but delivers no flow
✗ Automatic alarm or machine stop
Flow monitor (ChemTec FAV/LCA)
✓ Whether the liquid is flowing above the setpoint
✓ Loss of flow due to blockage or leak
✓ Direct switching output for PLC or alarm
✓ Automatic machine stop signal when there is no flow
✓ Visual local indication (with acrylic version)
✓ 24/7 monitoring, including unattended operation
Pressure says nothing about flow when a nozzle is blocked
A blocked coolant nozzle is one of the most common causes of unnoticed tool failure and workpiece rejection in the machining industry. The pressure in the main line remains normal because the pump simply keeps running. The flow monitor in the coolant line to the spindle or machining point signals the reduction in flow immediately and stops the machine before the tool breaks or the workpiece burns.
What goes wrong without flow monitoring in cooling and lubrication
In the machining industry, the consequences of insufficient cooling or lubrication are direct and costly damage. That is precisely why flow monitoring in these systems is not a luxury but a basic operational requirement.
CNC milling machine / machining centre
Tool breakage due to overheating
Without coolant at the cutting point, the temperature of the tool and workpiece rises rapidly. A higher cutting temperature leads to accelerated wear, dimensional deviation due to thermal expansion and ultimately cracking or breakage of the tool. A broken cutter in a workpiece costs not only the tool but also the workpiece and downtime for milling out the broken tool.
Water-cooled spindle
Spindle bearing failure due to overheating
Cooled spindles rely on a continuous flow of cooling water to keep the bearings at temperature. If the cooling water flow fails, the bearing temperature rises rapidly. Overheating of spindle bearings leads to premature failure. A spindle repair or replacement costs tens to hundreds of thousands of euros, depending on the type of machine.
Hydraulic unit / central lubrication
Dry bearings due to lubrication stoppage
Central lubrication supplies guideways, ball bearings and ball screws with lubricant. In the event of a fault in the lubrication line, the machine keeps running while the lubrication points run dry. The damage accumulates invisibly until bearings or guideways seize or wear play becomes visible in the dimensional accuracy.
Laser and EDM equipment
Thermal damage to optics or electrodes
Laser cutting machines and spark erosion equipment cool critical components with deionised water or process cooling water. If the cooling flow fails, optical components, laser sources or spark electrodes quickly heat up, resulting in immediate and irreparable damage.
Applications in the manufacturing industry
Flow monitoring in cooling systems and machine lubrication covers a wide range of applications in the manufacturing industry. Any application in which a liquid flow performs a critical function and failure causes immediate damage to the machine or workpiece is a candidate for a flow monitor.
CNC coolant to the cutting point
Monitoring whether coolant reaches the nozzle. In the event of a loss of flow, the flow monitor gives a digital signal to the CNC control for an emergency stop or alarm. Suitable for water-based emulsions and oil cooling.
Spindle cooling
Monitoring of the cooling water flow through the spindle jacket. If the flow decreases due to blockage or pump failure, the spindle stops automatically before the bearings overheat.
Central lubrication and minimum quantity lubrication (MQL)
Monitoring of the lubricant flow to guideways, bearings and ball screws. In MQL (Minimum Quantity Lubrication) systems, the flow rate is extremely low and therefore particularly sensitive to blockages.
Flow cooling of electric motors and drives
Large servo drives and spindle motors are cooled internally or externally. A flow monitor in the cooling water line checks whether the cooling capacity is sufficient and switches off the drive in the event of failure before the thermal protection intervenes.
Laser cooling (deionised water)
Laser sources and optics are cooled with deionised water. The LPH series without seals in the fluid path is ideally suited to this: no contamination of the DI water by leaking seals.
Hydraulic cooling circuit
Hydraulic units generate heat. A cooling circuit with a heat exchanger cools the hydraulic oil. A flow monitor in the cooling water line checks whether the cooling capacity is active, so that the oil does not overheat and lose viscosity.
Which ChemTec flow monitor for cooling and lubrication?
For cooling systems and lubrication applications in the manufacturing industry, four ChemTec series are relevant, depending on the medium, the flow rate and the desired flexibility of the setpoint.
| Series | Type | Application | Medium / Material | Setpoint |
|---|---|---|---|---|
| FAV Series | Adjustable, higher cooling water flows | Spindle cooling, motor cooling, hydraulic cooling circuits | Water 0.4–75 LPM. Brass or 316 stainless steel. Max. 3,000 PSIG for stainless steel. | Adjustable on site, ratio ≥ 10:1 |
| LCA Series | Adjustable, economical | Central lubrication, cooling water circuits, water treatment | Corrosive and non-corrosive liquids. Economical version. | Adjustable on site, ratio ≥ 10:1 |
| LPH Series | Non-adjustable, deionised water | Laser cooling, dialysis, analytical instruments | No seals in the fluid path. Acrylic, brass, 316 stainless steel or Teflon. | Fixed per model number |
| FS Series | Non-adjustable, higher flows | Cooling towers, heat pumps, cooling systems with higher flows | No seals, one moving part, vertical inline. 316 stainless steel, brass or PVC. | Fixed per model number |
PLC integration and stop logic
The switching output of a ChemTec flow monitor connects directly to a digital input of the CNC control or PLC. The stop logic is simple and reliable: as soon as the flow monitor opens its switching contact on loss of flow, the control receives a signal and responds with a pre-programmed action.
In CNC machining centres, the most common implementation is linking the coolant flow monitor to the spindle start condition. The spindle may only start if coolant flow is present, and stops automatically if the flow drops out during machining. This prevents the operator from forgetting to switch on the coolant and also protects the machine against unexpected faults in the cooling system during unattended production.
Flow monitor in series with the spindle start
The most effective implementation in a CNC environment is the flow monitor as an interlock in the spindle start conditions: the spindle only starts if coolant flow is present (NC contact closed), and stops immediately if the coolant flow drops out. This requires only one digital input in the control and no additional program logic besides the standard interlock function. On the FAV and LCA, the flow monitor setpoint is field-adjustable, so that the switching threshold can be set exactly to the minimum required flow rate.
For minimum quantity lubrication (MQL) or central lubrication systems, the logic is similar: the machine does not start if the lubrication confirmation is missing, and stops when a loss of flow is detected. With multiple lubrication points that each need to be monitored, several flow monitors are included in series or in parallel in the interlock chain.
Selection in four questions
| Question | Answer and recommendation |
|---|---|
| What is the normal flow rate of the system? | Determine the normal process flow in LPM (liquid) or SLPM (gas). Choose an FAV or LCA for which the normal flow is at least 10 times the desired switching setpoint. For lower flows: CCM series. |
| What is the medium? | Water-based coolant or emulsion: FAV brass or stainless steel. Deionised water (laser cooling): LPH without seals. Oil (lubrication, hydraulic): FAV or LCA brass or stainless steel. Corrosive coolant: FAV or LCA stainless steel or inert CCM. |
| Is the setpoint known in advance and stable? | Unknown or variable: choose FAV or LCA (adjustable on site). Stable and known: choose LPH or FS (fixed setpoint, ready for direct installation, no adjustment needed). |
| How is the output used? | Digital input of CNC control or PLC: connect the switching contact of the FAV, LCA, LPH or FS directly to the DI card. Local visual indication: choose a version with an acrylic element (visual float). Both: FAV or LCA with acrylic sight glass and electrical contact. |
Keep the pressure gauge as a supplement
The pressure gauge does not need to be removed. Pressure and flow monitor complementary quantities. The pressure gauge signals pump failure or a line break through a drop in pressure. The flow monitor signals blockage, too low a flow and loss of flow due to a leak further down the line. Together, they give a complete picture of the status of the cooling or lubrication system.
ChemTec flow monitors for cooling and lubrication at Inacom
Inacom supplies the ChemTec FAV, LCA, LPH and FS series for cooling systems and lubrication applications in the manufacturing industry. Advice on series selection, setpoint range and material compatibility with your coolant or lubricant is available via inacom.nl.
ChemTec LPH UHP series at Inacom
Inacom is the official ChemTec distributor for the Dutch market. The LPH UHP series is available in several connection configurations (½" MVCR, ¼" and ⅜" weld/tube stub) with electropolished 316L stainless steel and cleanroom packaging. Selected configurations are available within 24 hours. Contact us via inacom.nl/contact/ for current availability, express deliveries and technical advice.
