For a car wash gantry on its own, a compressor delivering 400 to 600 L/min at 8 bar is enough in most cases. If the gantry washes a few cars a day, an E 75 piston compressor will do. If it runs cycle after cycle all day, a variable speed screw compressor such as the S 55, or the K 75 4-in-1 if the plant room is small, copes better over time.
What does compressed air do on a gantry?
On a gantry, air does not wash the car: it drives the machine. It moves the cylinders that press the side brushes and the roof brush against the car, opens and closes the chemical valves, and often feeds the dosing pumps and the active foam generator. If pressure drops mid-cycle, the brushes lose contact and the programme can stop on a fault.
So a gantry does not use air continuously. It uses a lot during a cycle, then almost nothing between two cars. That profile drives the choice. Our page on compressors for car washes covers the whole site, including jet wash bays and service points. Here we focus on the gantry.
Sizing step by step
Step 1: flow during the cycle. It is in the gantry manufacturer's manual. As a rough guide, the usual order of magnitude is 200 to 300 L/min during a cycle. We take 250 L/min for this example.
Step 2: required pressure. The manual also gives the supply pressure. A compressor set to 8 bar leaves headroom above what most cylinders and valves need.
Step 3: margin. Add at least 25 % for cylinder seal wear and small leaks, which are common in a wet environment: 250 × 1.25 = 312 L/min, about 315 L/min.
Step 4: duty. Work out how long the gantry runs in the busiest hour. Take a 5 minute cycle, a value chosen for this example, and 6 cars in the peak hour: the gantry runs 30 minutes out of 60, or 50 % of the time. On a busy Saturday it can run almost non-stop.
That last figure decides the technology more than the flow itself.
Which compressor for your gantry?
A few cars a day: the E 75 piston compressor
The E 75 piston compressor, 7.5 kW delivers 0.9 m³/min, or 900 L/min, on a 180 L receiver, at 8 or 12.5 bar. For 315 L/min during the cycle, it fills its receiver quickly and then stops. A piston compressor likes this rhythm: it needs rest time between cycles. It is the right choice for a stand-alone gantry or a small site.
Back-to-back cycles all day: the S 55
When the gantry runs half the time or more, demand becomes continuous. The S 55 screw compressor, 5.5 kW delivers 0.6 m³/min at 8 bar, or 600 L/min, and is built for continuous duty. It has variable speed: it slows down between two cars instead of stopping and restarting all the time. It comes without receiver or dryer. Add a receiver sized with our air receiver size calculator and a refrigerated dryer for 5.5 and 7.5 kW compressors.
Small plant room: the K 75 4-in-1
The K 75 4-in-1 screw compressor, 7.5 kW combines the screw unit, a 420 L receiver, the refrigerated dryer and filtration in one frame. It delivers 1.1 m³/min at 8 bar. It covers the gantry with spare capacity for one or two bays added later, and avoids fitting three units into a small room. Our article 4-in-1 or standalone compressor compares both layouts.
| Gantry use | Recommended model |
|---|---|
| A few cycles a day | E 75, piston, 0.9 m³/min, 180 L receiver |
| Back-to-back cycles, room to spare | S 55, screw, 0.6 m³/min at 8 bar, plus receiver and dryer |
| Back-to-back cycles, small room, future extension | K 75, 4-in-1, 1.1 m³/min at 8 bar |
Pitfalls specific to gantries
- Water in the cylinders. A gantry lives in steam and spray. Condensate from the compressor adds to that moisture, washes the grease out of the cylinders and makes the valves stick. A dryer is not optional. Our article which air dryer to choose helps you choose between refrigerated and desiccant if some pipes run through the cold.
- The plant room. Keep the compressor out of the wash area, in a ventilated, frost-free room away from chemical vapours. Our article on the compressor room gives the basic rules.
- Draining. At night nobody watches the site. An automatic condensate drain empties the receiver for you. Condensate contains oil: route it through an oil/water separator before discharge, in line with local regulations.
- Power supply. The E 75, S 55 and K 75 run on three-phase power. Check the capacity available at your switchboard before ordering.
For the whole site, go back to our page on compressors for car washes or use the configurator. Then send us your gantry manual with a quote request: we will check flow and pressure with you.
For your trade: Compressor for car washes.