Proportional Valves and Hydraulic Valves: Types, Applications and Sourcing Guide

Every hydraulic machine — an excavator, a loader, a tractor, a hydraulic power unit, a variable-displacement pump — is steered by valves. Two families do most of the work: proportional valves, which convert an electrical signal into continuously variable flow or pressure, and hydraulic valves, the broader family of directional, pressure, flow and cartridge valves that route and protect the oil.

This guide explains how each family works, how they differ, which applications they suit, and — most importantly for buyers — what to confirm before placing an order. It also lists the current FOB Auto Parts range with real part references.

What Is a Proportional Valve?

A proportional valve turns an electrical input, normally a variable current, into a continuously variable hydraulic output. Instead of snapping to "fully open" or "fully closed", the spool or poppet moves to a position that is proportional to the coil current. Turn the current up and the spool strokes further; hold it steady and the spool holds that position.

Three characteristics separate a proportional valve from an ordinary on/off solenoid valve:

• Continuous positioning — the spool can sit at any intermediate position, not just the two end stops.
• Current-to-output relationship — output force rises with coil current, so flow or pressure can be dialled in rather than simply switched.
• Ramp and dither control — a proportional amplifier can add ramps and a dither signal, which smooths acceleration and reduces shock in the circuit.

Main types of proportional valve

• Proportional directional valves — control both the direction and the amount of flow sent to an actuator. Typical of boom, arm, bucket, steering and travel circuits on mobile machinery.
• Proportional pressure valves — reducing, relieving and pump-control valves that set system pressure continuously. The classic application is variable-displacement pump control, where the valve strokes the pump swashplate so pump output follows demand.
• Proportional flow (throttle) valves — regulate actuator speed, often with pressure compensation so speed stays steady as the load changes.
• Proportional cartridge valves — screw-in cartridges that bring proportional control to compact manifold blocks and higher flows.

The FOB Auto Parts Proportional Valve Range

Our proportional valve programme covers two groups: general proportional solenoid valves, and a flagship series of pump-control proportional valves designated KDRDE5K and KWE5K. Every unit is supplied with the matching solenoid coil and connector.

ACD110-A Proportional

OE ref: ACD110-AFOB-2100-A

A proportional solenoid valve from the ACD110 family, used to modulate flow or pressure in a hydraulic circuit in proportion to coil current. The ACD110-A and ACD110-B variants let a machine builder fit the same valve body to two different circuit layouts.

ACD110-B Proportional

OE ref: ACD110-BFOB-2100-B

The companion variant to the ACD110-A, sharing the same proportional control principle. Ordering both references together gives a matched pair for circuits that need two proportional functions.

702-21-57400 Proportional

OE ref: 702-21-57400FOB-2530-A

A proportional solenoid valve for general hydraulic control duty. Supplied as a complete assembly with coil, ready for manifold or in-line mounting.

KDRDE5K-20/30C12A-111-T Flagship

OE ref: KDRDE5K-20/30C12A-111-TFOB-3089-A

Part of the flagship pump-control series. These KDRDE5K valves are the proportional solenoid valves that mount on variable-displacement hydraulic pumps and manifold blocks to stroke the pump and set output flow. The dash suffix encodes nominal size, spool configuration and electrical connection.

KDRDE5KR-20/40C07-203A-T Flagship

OE ref: KDRDE5KR-20/40C07-203A-TFOB-3082-B

Flagship-series proportional valve with the "R" designation, covering the 20/40 nominal-size range. Used where a pump-control or manifold-mounted proportional function must hold a stable setting across a wide flow band.

KWE5K-31/G24YA30 Flagship

OE ref: KWE5K-31/G24YA30FOB-3093-B

KWE5K proportional solenoid valve from the flagship series. The "G24" in the reference denotes a 24 V DC coil — the standard supply on mobile and industrial equipment — with the trailing characters defining the spool and connector arrangement.

Full proportional valve reference list

What Is a Hydraulic Valve?

"Hydraulic valve" is the umbrella term for any valve that controls the direction, pressure or flow of hydraulic fluid. In practice the family breaks down into five groups:

• Directional control valves — 2/2, 3/2, 4/2 and 4/3 valves that start, stop and reverse flow to an actuator. They may be spool or poppet type, and actuated manually, by solenoid, or proportionally.
• Pressure control valves — relief, reducing, sequence and counterbalance valves that cap system pressure or hold a load.
• Flow control valves — throttle, priority and flow-divider valves that set actuator speed or split a pump's output between two circuits.
• Cartridge valves — screw-in or slip-in cartridges that deliver directional, pressure or flow functions inside a compact manifold block, often at higher flow than a conventional subplate valve of the same envelope.
• Check and shuttle valves — one-way elements that prevent reverse flow, hold a load, or select the higher of two pressures.

Solenoid-operated directional valves are the most common service item on this list. When they fail, the symptom is usually a function that stops responding, moves slowly, sticks in one direction, or heats its coil — which is why coil voltage, coil resistance and connector type matter as much as the valve body itself.

The FOB Auto Parts Hydraulic Valve Range

Our hydraulic valve programme covers directional solenoid valves, cartridge valves and the solenoid coil assemblies that drive them, supplied for both OE replacement and series production.

DHF10-232A Hydraulic

OE ref: DHF10-232AFOB-2130-A

A hydraulic directional valve from the DHF10 series. The "232" designation follows the common directional-valve naming convention, where the digits describe the number of ports and the number of spool positions.

4099 6168 Hydraulic

OE ref: 4099 6168FOB-2780-A

A hydraulic solenoid valve for directional control duty. Available as a complete assembly or as a body-and-coil kit for repair work. A "B" variant with the same body family is listed below.

20141544 Hydraulic

OE ref: 20141544FOB-2790-A

A hydraulic solenoid valve covering equipment that runs the 20141544 reference. Supplied with a matching coil and connector so the valve can be fitted without re-terminating the harness.

17YJ90048 Hydraulic

OE ref: 17YJ90048FOB-2781-A

A hydraulic valve from the 17YJ90048 family, used on mobile hydraulic circuits. A 24 V version of the same family is available as 17YJ90048-24V (FOB-2781-B).

4099 6168-B Hydraulic

OE ref: 4099 6168-BFOB-2780-B

The "B" variant of the 4099 6168 family. Fitting the correct variant matters: the two references share a body family but differ in electrical or spool detail, so always quote the full reference including the suffix.

4089577 Hydraulic

OE ref: 4089577FOB-1906

A hydraulic valve covering the 4089577 reference. Supplied ready for manifold or in-line installation with a matched coil.

0 928 400 617-12 Hydraulic

OE ref: 0 928 400 617-12FOB-2470-12

A hydraulic valve covering the 0 928 400 617-12 reference, supplied as a complete unit with coil. The "-12" suffix indicates the electrical variant, so quote the full reference including the suffix when ordering.

Full hydraulic valve reference list

Proportional Valve vs. Hydraulic On/Off Valve

Sourcing Checklist: What to Confirm Before Ordering

Hydraulic valves are frequently mis-ordered because two references that look alike differ only in coil voltage or connector type. Confirm the following before you send an enquiry:

Where These Valves Are Used

• Mobile hydraulics — excavators, wheel loaders, backhoes, cranes, telehandlers and skid steers, where proportional control feathers boom, bucket and steering functions.
• Agricultural machinery — tractors, harvesters and implements, including the brake, clutch and auxiliary hydraulic circuits.
• Hydraulic pump control — variable-displacement pumps in mobile and industrial power packs, where a proportional valve strokes the pump to match output to demand.
• Industrial power units — presses, injection moulding machines, machine tools and test rigs where pressure and speed must be set rather than merely switched.
• Material handling and lifting — forklifts, lift tables and winches, where load holding and controlled lowering are both required.

Frequently Asked Questions

What is the difference between a proportional valve and a servo valve?

A servo valve gives faster dynamic response and tighter control at the cost of a higher price and far greater sensitivity to fluid contamination. A proportional valve trades some response speed for robustness, a simpler circuit and a much lower cost, which is why it is the default choice on mobile machinery and on most industrial power units. If your circuit needs closed-loop position control at high bandwidth, specify a servo valve; if it needs smooth, repeatable, economical metering, specify proportional.

Can a proportional valve replace an on/off valve?

Often yes — provided the flow and pressure ratings match, the mounting interface is the same, and a proportional amplifier is added to the circuit. What you should not do is remove a hard on/off or check element that provides positive isolation or load holding: proportional valves are for metering, not for safety isolation.

Which coil voltage should I order?

24 V DC is the most common supply on mobile equipment and industrial machinery; 12 V DC is common on smaller machines and on automotive-derived systems. The voltage is encoded in the reference on many valves — for example the "G24" in KWE5K-31/G24YA30 indicates a 24 V DC coil. If the old coil is still readable, quote the voltage marked on it.

Do you supply the solenoid coil separately?

Yes. We supply complete valve assemblies, and also coils and coil assemblies as service parts, including the connector. Repair shops in particular often need the coil only, and matching the coil to the valve body is the single most common cause of a "new valve that still does not work".

Can you cross-reference my OEM number?

Yes. Send the OE or manufacturer reference — including any suffix — plus a photograph of the valve and its connector, and we will confirm the corresponding FOB Auto Parts code and coil. Where a reference falls outside the ranges listed above, we will tell you plainly rather than substitute a similar-looking valve.

What are your MOQ and lead times?

MOQ and lead time depend on the reference and on whether it is a stock line or made to order. Send the part numbers and quantities and we will reply with an offer including the lead time.

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