High Pressure Pump Selection for OEM and Car Wash Systems

Most premature pump failures are not caused by a bad pump but by a pump that was wrong for the duty: run too fast for a 16-hour car wash cycle, starved at the inlet, fitted with a brass head and fed chloride-rich recycled water, or driven through an unloader sized for half the flow. Getting high pressure pump selection right at the design stage costs a few hours of calculation; getting it wrong costs seal kits, valves and reputation for the life of the product. This guide sets out a repeatable method for OEM integrators and car wash system builders: define the duty, size pump and motor with standard formulas, choose rpm and drive, match shaft and mounting, pick the head material, size the valves and check inlet conditions. It closes with a table mapping the Fussen A to E series plunger pumps to typical OEM applications.

Step 1: Define the duty before you look at a catalog

A plunger pump is a positive displacement machine: flow is set by displacement and speed, pressure by the restriction downstream. State the duty in both terms, plus everything that affects life.

• Working pressure (bar) at the nozzle plus line losses: a 20 m, 3/8 inch hose at 20 L/min loses 10 to 20 bar; a car wash boom with a long underground run, 20 to 40 bar. Specify pressure at the pump outlet, not at the gun.
• Flow (L/min): the sum of all nozzles that can be open at once, plus 5 to 10 percent for nozzle wear.
• Hours per day and duty cycle: a washer that runs 2 hours a day and a self-serve bay pump cycling 12 hours a day in 30-second bursts need different rpm, valve types and seals.
• Water quality: mains, well, recycled or softened; chlorides, solids, and whether chemicals pass through the pump or are injected downstream.
• Inlet temperature: standard seals are typically rated to about 60°C; hotter feed needs a high temperature seal kit and lower rpm.
• Prime mover: three-phase or single-phase electric, petrol or diesel engine, hydraulic motor or PTO.

Write this down as a one-page duty sheet; every later decision comes from it.

Step 2: High pressure pump selection formulas for pump and motor sizing

Hydraulic power is the product of pressure and flow. In catalog units:

Hydraulic kW = bar × L/min ÷ 600

Shaft power is higher, because a triplex plunger pump converts mechanical to hydraulic power at roughly 85 to 90 percent efficiency once valve, seal and crank losses are included:

Motor kW = (bar × L/min ÷ 600) ÷ η_pump, with η_pump = 0.85 to 0.90

Belt drives lose a further 3 to 5 percent, so divide again by 0.95 for a pulley drive. Then round up to the next standard motor frame; a practical rule is 10 to 15 percent more power than the calculated shaft figure, to cover the unloader setting, voltage dips and wear.

Worked example: a two-bay car wash

Two bays with size 05 nozzles at 150 bar can be open together. A 05 nozzle passes 14.0 L/min at 150 bar, so the pump must deliver 28 L/min plus wear margin, say 30 L/min, at 170 bar after 20 bar of line loss. Hydraulic power is 170 × 30 ÷ 600 = 8.5 kW; at 88 percent efficiency that is 9.7 kW at the shaft, so the next standard motor is 11 kW. A FBS 3020 (30 L/min at 200 bar) or FCC 3030 fits this duty with headroom.

Step 3: Choosing the pump rpm

A given flow can be reached with a small pump running fast or a larger pump running slowly. Catalog ratings are usually at 1450 rpm (4-pole motor, 50 Hz) or 1750 rpm (60 Hz), with lower-speed ratings at 1000 rpm (6-pole) and 750 rpm (8-pole or reduction drive).

Speed governs life more than any other choice: seal, plunger and valve wear are all proportional to rpm, and inlet conditions get harder as the plunger has less time to fill the cylinder. The rules of thumb:

• 1450/1750 rpm: compact, lowest cost, direct coupling to a 4-pole motor. For intermittent duty up to 4 to 6 hours a day on clean water.
• 1000 rpm: a larger pump for the same flow, but seal and valve life roughly 40 to 50 percent longer, quieter, and more tolerant of marginal inlet conditions. The usual choice for car wash pump rooms and any duty above 8 hours a day. Flow scales with speed: a pump rated 21 L/min at 1450 rpm gives 14.5 L/min at 1000 rpm at the same pressure.
• 750 rpm and below: continuous duty, hot water, recycled water with solids, or a once-a-year service window. Achieved with an 8-pole motor, belt reduction or gearbox.

When the duty sheet says 12 hours a day, take the pump one frame up and run it slower; the extra cost is repaid in seal kits.

Step 4: Drive options and shaft sizes

Drive arrangement is decided together with rpm, because each suits a speed range and a prime mover. Fussen pumps use industry-standard shaft diameters, so a machine designed around them accepts the pump as a drop-in.

Matching shaft to pump series

Shaft diameter steps with torque. A, B and C series pumps use a Ø24 mm solid or Ø28 mm hollow shaft; the D series moves to Ø30 mm, the E series to Ø40 mm, the FFS to Ø50 mm and the gearbox FFS-G to Ø60 mm. Shaft torque is about 9550 × kW ÷ rpm, so 30 kW at 1450 rpm is 198 Nm, comfortable on Ø30 mm; the same power at 750 rpm is 382 Nm and needs the larger shaft.

Gearbox versions for engines

Engines run at 1800 to 3600 rpm while the pump wants 750 to 1450, so an engine-driven unit needs reduction. The FEK-G gearbox plunger pump at 450 to 750 bar, the FES-G at 1500 to 2000 bar and the FFS-G at 800 to 1500 bar integrate the reduction on the pump, so the engine couples directly. The FEK-G lists paired models such as FEK-G 4060 and FEK-G 3060: the same 600 bar pump at two ratios giving 40 or 30 L/min, so the OEM can match an engine’s rated speed without changing the hydraulic end.

Step 5: Pump head material by media

The manifold material should follow the water analysis, not the price list.

• Brass (Fussen FAB, FBB, FCB, FCC, FCR): the standard for clean mains water and the most economical. Not recommended for softened or recycled water with chlorides, or continuous duty above about 60°C, where dezincification erodes the manifold.
• Nickel-plated brass (FAN, FBN, FCN, FCK, FCM): the plating resists detergents, waxes and mildly aggressive water. The best cost-to-durability ratio for most commercial car wash pump sets.
• Stainless steel (FAS, FBS, FCH, FCL, FDH, FDK, FDL, FEK, FES, FEL, FFS): required for seawater, deionised water, hot water, acids and alkaline cleaners passing through the pump, and for food and pharmaceutical sites. All Fussen D and E series pumps are stainless because fatigue strength is also needed at those pressures.

In every case the plungers are solid ceramic and the valves stainless; seal kits are chosen separately for cold, hot or chemical service.

Step 6: Unloader, regulating valve and safety valve

When the trigger closes, the unloader or regulating valve diverts full flow to bypass at a controlled pressure; without it, pressure rises until something breaks. Three rules:

1. Size by flow, not by pressure. Passing 30 L/min through a valve rated for 21 L/min raises the pressure spike on trigger closure and overheats the valve in bypass. Choose a valve rated for at least the pump’s flow plus 10 percent.
2. Match the valve type to the duty cycle. A trapped-pressure unloader suits washers and single-gun systems. A pressure regulating valve with permanent bypass is better for multi-gun systems and car washes where outlets open and close independently; pneumatic or electric control suits automated equipment.
3. Fit a separate safety valve. The unloader is a control device; the safety valve is a protection device set 10 to 15 percent above working pressure and sized for full pump flow.

Fussen supplies its FV series unloaders, regulating valves and safety valves in ranges matched to each pump series, and recommends specifying valve and pump together. In bypass the water heats by roughly 1.5 to 2°C per pass, so on a car wash with long idle periods add a thermal dump valve opening at about 60°C.

Step 7: Inlet conditions and booster pumps

More plunger pumps are damaged by the inlet than by the outlet. If the cylinder does not fill completely on the suction stroke, the water column separates and slams back on the pressure stroke; this cavitation destroys valves and seals within weeks. Design the suction side to these rules:

• Inlet pressure of 1 to 4 bar measured at the pump inlet while running; hot water and high speed need the upper end.
• Suction line one size larger than the inlet port, short, with no elbows within 10 pipe diameters of the pump.
• A 50 to 80 mesh strainer with a gauge or vacuum switch after it to detect blockage.
• A float-valve feed tank holding 2 to 3 minutes of pump flow for any pump above 20 L/min or unreliable mains.
• A low-pressure or float switch that stops the pump on loss of feed.

Where the feed cannot meet these figures, fit a centrifugal booster delivering 2 to 3 bar at 120 percent of plunger pump flow. It is standard on car wash pump rooms, hot water units and any pump above 1000 rpm fed from a floor-level tank; for the FDL and FEL high flow pumps it is mandatory.

Car wash specifics: multi-bay, detergents and duty cycle

• One pump per bay or one central pump? A central pump serving several bays is cheaper but runs in bypass whenever a bay is idle, and one failure closes every bay. Above three bays most operators specify one pump per bay or per two bays. Self-serve bays typically use 15 to 21 L/min at 100 to 150 bar; an A series pump such as the FANH hollow shaft nickel-plated pump flange-mounted on a 6-pole motor is a common building block.
• Detergents. Inject downstream of the pump wherever possible; if chemicals must pass through it, use nickel-plated or stainless heads and check seal compatibility.
• Automatic tunnels. Arches with 20 to 40 nozzles draw 60 to 150 L/min at 60 to 100 bar, the territory of the FCR high flow pump or the FDL at up to 150 L/min on a 6-pole motor.

Mapping Fussen pump series to OEM applications

Model numbers give flow first, then pressure (FBS 3020 = 30 L/min, 200 bar; FDH 15100 = 15 L/min, 1000 bar).

To turn this into a firm selection, send your duty sheet and prime mover details to Fussen through the contact page; the engineering team will confirm pump model, rpm, shaft, valve set and inlet requirements, and can supply drawings for the frame and coupling design.

Frequently asked questions

Can I run a plunger pump at a lower speed than its catalog rating?

Yes, and it is usually beneficial. Flow falls in proportion to speed and the pressure rating is unchanged, so a pump rated 21 L/min at 1450 rpm gives about 14.5 L/min at 1000 rpm with the same 250 bar capability. Do not exceed the catalog maximum speed, and at very low speeds confirm with the manufacturer that splash lubrication is still adequate.

What is the difference between an unloader and a safety valve?

An unloader or regulating valve controls working pressure and diverts flow when the outlet closes; it operates every cycle. A safety valve is set above the working pressure, should never open in normal use, and protects the system if the unloader fails. Both are required and both must be rated for the full pump flow.

When do I need a hollow shaft pump instead of a solid shaft?

A hollow shaft pump such as the Fussen FABH, FANH or FASH mounts directly on the motor shaft and flange, eliminating coupling and alignment. It is the standard choice for compact electric washers and car wash sets up to about 21 L/min and 250 bar. Solid shafts serve belts, engines and larger pumps.

How much inlet pressure does a high pressure plunger pump need?

Between 1 and 4 bar measured at the inlet port while running at full flow. Gravity feed is not sufficient for most pumps above 1000 rpm or 20 L/min. Where mains pressure is unreliable, hot water is used or the pump is large, fit a centrifugal booster delivering 2 to 3 bar at about 120 percent of the plunger pump's flow.