Winterising Industrial Pressure Washers: The Complete UK Freeze-Protection Protocol

Across the UK, the arrival of the first sharp November frost brings a predictable surge in catastrophic equipment repairs. A single night with temperatures dipping to $-3^\circ\text{C}$ is sufficient to freeze stagnant water trapped inside a pressure washer pump, unloader valve, or heating coil.

Because water expands by $9%$ in volume upon crystallisation, it generates hydrostatic stresses exceeding $2,000\text{ bar}$ — easily fracturing forged brass manifolds, snapping ceramic plungers, and bursting heavy steel coil windings.

Here is the professional winterisation procedure that Alkota engineers recommend for stationary wash bays, mobile trailers, and unheated plant sheds.

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The Two Winterisation Methods: Why Glycol Circulation is Superior

Many operators attempt to winterise machines using an airline blow-out gun. While blowing compressed air through the system removes some water, surface tension and coil gravity traps leave pockets of water in bottom coil loops and valve cavities that subsequently freeze and crack.

The Recommended Method: Propylene Glycol Antifreeze Circulation

[1. Disconnect Water Inlet]
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[2. Prepare 50/50 Monopropylene Glycol Mix (Rated to -35°C)]
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[3. Insert Short Suction Hose into Antifreeze Drum]
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[4. Remove Spray Nozzle / Attach Open Gun Lance]
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[5. Run Unit at Low Idle Until Coloured Glycol Discharges]
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[6. Cycle Trigger 3 Times to Flood Unloader Bypass Circuit]
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[7. Shut Down & Depressurise: System is 100% Protected]

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Step-by-Step Workshop Procedure

Step 1: Chemical & Fuel Isolation

1. Ensure the detergent metering valve is closed.
2. For hot water diesel-fired units, ensure the burner switch is OFF and the heating coil has cooled completely to ambient temperature.

Step 2: Prepare the Antifreeze Solution

• Use Monopropylene Glycol (RV / Marine / Industrial non-toxic grade) diluted with clean water to a $50/50$ ratio. This provides freeze protection down to $-35^\circ\text{C}$ while lubricating pump packings and preventing internal corrosion.
• Note: Avoid automotive ethylene glycol in food-processing or agricultural environments due to toxicity.

Step 3: Draw Antifreeze Through the Machine

1. Connect a 1.5-metre length of reinforced suction hose to the pump inlet and submerge the open end in a 25-litre drum of antifreeze solution.
2. Remove the spray nozzle from the lance (to reduce backpressure) and direct the lance back into the antifreeze container for fluid recovery.
3. Start the engine or electric motor.
4. Pull the trigger to open the high-pressure circuit.
5. Run the unit until pure coloured antifreeze solution discharges smoothly from the lance tip.

Step 4: Protect the Unloader Valve & Chemical Injector

1. While fluid is flowing, rapidly release and pull the trigger gun 3 to 4 times. This forces antifreeze through the unloader bypass loop and relief passages.
2. Open the chemical metering valve for 5 seconds to draw antifreeze through the downstream injector.
3. Switch off the machine and pull the trigger once more to relieve any residual hydraulic line pressure.

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Spring Commissioning (De-Winterising)

When returning the machine to service in spring:

1. Connect your standard water supply.
2. Direct the open lance into an empty container.
3. Run the machine for 60 seconds to flush the glycol back into the container for reuse next winter.
4. Re-fit your spray nozzle and inspect all fittings for leaks before initiating the burner circuit.