Solenoid Valves: How They Work, Key Types, and Real-World Uses

A solenoid valve is small, but it can stop a machine, protect an engine, or keep a hydraulic circuit under control. In this guide, we’ll break down how these valves work, where they are used, and how to choose the right replacement for heavy equipment and industrial systems.

 

Key Takeaways

• A solenoid valve is an electromechanical device used to start, stop, or direct the flow of liquid or gas with an electric signal.
• Normally closed valves prevent flow when de-energized, while normally open valves allow flow when de-energized.
• Direct acting valves move the main orifice directly; pilot operated valves use system line pressure to handle larger flow with low control power.
• Common solenoid valve applications include excavator hydraulic circuits, diesel fuel shutoff, air brake systems, and water or coolant control.
• Choosing the right valve improves safe switching, uptime, high reliability, and long service life across fleets and industrial applications.

 

What Is a Solenoid Valve?

A solenoid valve controls liquid or gas flow by using electrical energy to move a mechanical part. It consists of a coil, plunger, and sleeve assembly, plus a spring, seal, and valve body that guide the fluid through the ports.

 

The basic solenoid valve function is simple. When the solenoid coil is energized, the coil creates a magnetic field that moves the plunger and changes the valve from its normal resting position. Energizing the coil raises the plunger to allow flow in many common designs. When power is removed, the plunger return spring sends the plunger back to its default state.

 

That default state can be normally closed or normally open. Normally open and closed refer to the de-energized state, also called the unpowered state.

 

Typical media include:

• Hydraulic oil in excavators, loaders, and agricultural machines
• Diesel fuel in engine shutoff circuits
• Compressed air in pneumatic brake and actuator control
• Water and coolant in cooling loops
• Gas, steam, refrigerants, and process liquids in plant equipment

 

Solenoid valves manage water, air, gas, oil, steam, and refrigerants. They are essential for automated control systems because they are compact, fast, and easy to operate from relays, switches, or PLC outputs. That compact design matters when space is tight around engines, manifolds, and other components.

How Does a Solenoid Valve Function?

In a common normally closed valve, the valve starts in the closed position. The plunger return spring holds the plunger against the orifice, so the seal blocks the flow path. Energizing a normally closed valve opens the flow path because the magnetic field pulls the plunger away from the seat.

 

The main control elements are:

• Solenoid coil: a winding of wire that creates magnetic force when powered
• Plunger: the moving metal part actuated by the magnetic field
• Valve body: the housing that contains the inlet, outlet, orifice, and ports
• Orifice or seat: the opening where fluid can pass fluid through the valve
• Spring: the part that returns the plunger when the coil is de energized

 

The cycle looks like this:

1. The coil is de energized, and the valve stays in its normal position.
2. The control system sends voltage to the coil.
3. The energized coil creates a magnetic field.
4. The magnetic force moves the plunger with enough force to change the valve position.
5. The orifice opens or closes.
6. When power is removed, the spring returns the valve to its de energized state.

 

A normally closed valve stays shut without power. This is common for fuel shutoff and safety circuits. A normally open valve stays open without power, which is useful where fail-open operation is safer, such as some cooling or lubrication lines. Energizing a normally open valve stops the flow.

Key Types of Solenoid Valves

Solenoid valves come in several designs. The best choice depends on pressure, flow, media, voltage, temperature, duty cycle, and the particular application.

 

A normally closed valve is closed without power. Diesel engine fuel shutoff is a good example because the safe condition is often to shut fuel off. A normally open valve is open without power. Some cooling bypass circuits use this approach so coolant can keep moving if power drops.

 

Direct acting solenoid valves operate by using the coil to directly move the plunger, which opens or closes the main orifice. Direct acting valves are used for low flow capacities, low pressures, vacuums, or systems with little pressure difference. Direct-operated valves are suited for low pressures or vacuums, including suction lines, low-pressure lube lines, and test rigs.

 

Pilot operated valves work differently. The coil controls a small pilot passage, and fluid pressure from the pressure source moves a diaphragm, piston, or spool valve. Pilot operated valves use system line pressure to function, and pilot operated valves require a minimum pressure differential to function. This makes them useful for higher pressure and larger flow in pneumatic and hydraulic systems.

 

Solenoid valves can have two, three, or four ports:

Type	Plain meaning	Common use
2-way	Two ports and one flow path for fluid	General on off control
3-way	Three ports for fluid flow	Feed, shut, or vent an actuator
4-way	Controls air pressure in two directions	Pneumatic cylinders and double-acting actuators

 

2-way solenoid valves have one flow path for fluid. 3-way solenoid valves have three ports for fluid flow. 4-way solenoid valves control air pressure in two directions. Some manifolds use two solenoid valves in such a way that one side extends a cylinder while the other side retracts it.

 

Solenoid valves can operate at partial openings for proportional control. Proportional valves are used when the system needs more than a fully closed or fully open valve. Pulse Width Modulation can control flow rate in solenoid valves by switching the coil rapidly to create a controlled average position.

 

Direct Acting vs Pilot Operated

• Direct acting valves have fewer internal parts: coil, plunger, spring, valve body, and seat. Pilot operated designs add pilot passages, diaphragms, pistons, or a spool valve.
• Direct acting can operate at zero pressure differential, which helps with gravity-fed tanks, suction lines, and low-pressure test rigs.
• Pilot operated valves need a minimum pressure differential, often around 0.3–0.5 bar depending on the design, before they fully open. Always check the datasheet.
• Direct acting valves are usually better for small line sizes and fast response. Pilot operated valves are better when controlling larger flow and higher pressure with lower power consumption.

 

Before selecting either style, check manufacturer data for minimum pressure, maximum pressure, flow limits, Cv or Kv value, and duty cycle. The International Fluid Power Society is also a useful education resource for fluid power devices and hydraulic control basics.

 

Normally Closed vs Normally Open

Choose between normally open and normally closed configurations based on safety, energy use, and how the machine should behave during power loss.

Factor	Normally closed	Normally open
Default state	Closed valve in the unpowered state	Open valve in the unpowered state
Typical use	Fuel shutoff, emergency air shutoff, hydraulic lockout	Cooling, lubrication, some bypass lines
Energy use	Uses power while open	Uses power while closed
Safety behavior	Helps stop flow during failure	Helps keep flow moving during failure

 

In many mobile and plant systems, the valve state is chosen to match the safe condition of the machine, not just the easiest wiring layout. A normally closed fuel valve can prevent runaway fuel delivery. A normally open coolant valve can protect an engine or compressor from heat damage.

 

Solenoid Valve Applications in Heavy Equipment and Industry

Solenoids are found wherever fluid or gas needs automatic, remote, or timed control. That includes construction, mining, agriculture, trucking, factory utilities, and process control systems.

 

Common mobile equipment uses include:

• Fuel shutoff on diesel engines
• Hydraulic lockout for booms, buckets, and attachments
• Pilot control of directional valves
• Transmission oil control
• DEF dosing and emissions systems
• Air brake control in trucks and trailers

 

Industrial examples include compressed air distribution, water and coolant control in machine tools, process gas control, steam or hot water control, and automated washdown systems. Solenoid valves are used in irrigation, HVAC, automotive, and household appliances. Solenoid valves control water flow in dishwashers. Solenoid valves are used in automatic sprinkler systems. They regulate fuel flow in car engines. They control flow in medical devices and satellite propulsion.

 

In many application areas, solenoid valves handle on/off control, directional control, basic metering by timed open-close cycles, and pressure control when paired with regulators. In a pneumatic circuit, a 3-way valve may send air to an actuator and then vent it through an exhaust port. In hydraulic equipment, valves can route oil to cylinders that lift, tilt, steer, or lock a function.

 

Job sites are hard on parts. Dust, vibration, moisture, and temperature swings from −20 °C to +50 °C can shorten valve life. Rugged coils, sealed connectors, corrosion-resistant coatings, stainless steel, or brass bodies can help. IP/NEMA Ratings provide protection against dust and moisture, so check them when the valve will work outdoors or in washdown areas. NEMA explains enclosure protection basics through its enclosure ratings guidance.

Selecting the Right Solenoid Valve for Your System

Correct selection reduces leaks, nuisance shutdowns, and repeat repairs. Selecting a solenoid valve requires evaluating media type and pressure requirements before matching the electrical and mechanical details.

 

Review these points first:

• Fluid type: oil, water, air, fuel, coolant, gas, steam, or refrigerant
• Media compatibility: media compatibility is crucial for preventing corrosion in solenoid valves
• Operating pressure range: both minimum and maximum pressure matter
• Flow capacity: selecting solenoid valves involves considering flow capacity and electrical specifications
• Kv value or Cv value: the flow coefficient dictates fluid passage through a solenoid valve
• Temperature range: media and ambient temperature affect seals and coil life
• Default state: choose NC or NO based on safety behavior
• Ports and line size: solenoid valves can have two, three, or foure ports

 

Select solenoid valves based on Kv value and pressure range. A valve that is too small can restrict flow and create heat. A valve that is too large may respond poorly or fail to seal in low-flow service.

 

Electrical details are just as important. Voltage specifications must match the system's power supply requirements. Mobile equipment often uses 12 VDC or 24 VDC. Plant systems may use 120 VAC or 230 VAC. Also check connector style, wire length, coil duty rating, and whether the machine’s control system can supply the required current.

 

Example: replacing a 24 VDC fuel shutoff solenoid valve on a mid-size excavator. A mechanic should confirm the machine voltage, fuel pressure, line size, connector, mounting style, default state, and orifice size. If the original valve is normally closed, replace it with a normally closed unit unless the OEM documentation says otherwise.

 

Solenoid Valve Maintenance, Troubleshooting, and Replacement

Regular inspection can extend valve life and prevent downtime on job-critical equipment. Many industrial-grade valves last several million cycles, but heat, dirty fluid, vibration, and poor voltage can cut that life short.

 

Common symptoms include:

• Valve stuck shut or stuck open
• Slow response
• Coil overheating
• Buzzing or chattering
• Intermittent operation during vibration
• Leaks around the valve body or seal

 

Common causes include contaminated fluid, dirt, metal shavings, worn seals, corrosion, coil burnout from overvoltage, wrong voltage, or the wrong duty cycle. Low voltage can also stop the coil from making enough force to move the plunger.

 

Basic troubleshooting steps:

1. Listen or feel for a click when the valve is energized.
2. Measure voltage at the coil terminals.
3. Check coil resistance with a multimeter.
4. Inspect connectors, wire damage, and moisture.
5. Depressurize the system and inspect the plunger, seal, and orifice if safe.
6. Confirm the valve is not blocked by debris.

 

To replace a valve safely, isolate power, depressurize the line, label wiring, swap the valve or coil with a compatible unit, and pressure test before returning the machine to service. If the valve body is cracked, corroded, or badly worn, replacing the complete valve is usually smarter than repairing one part.

 

FAQ

Q1: How long does a solenoid valve usually last in heavy equipment?

A1: Lifespan depends on duty cycle, fluid cleanliness, temperature, vibration, and correct voltage. Many industrial-grade solenoid valves can last several million cycles under normal conditions. On excavators, loaders, and haul trucks that run daily, a well-specified valve can serve for years if filtration and wiring are in good shape.

 

Q2: Why does a solenoid coil get hot and is it dangerous?

A2: A coil warms up because it draws current. Excessive heat can mean overvoltage, a continuous-use job on an intermittent-duty coil, damaged insulation, or a partial short. Check the nameplate voltage, connector condition, and nearby contamination that may block heat dissipation. Replace coils that keep overheating.

 

Q3: Can I swap a normally closed solenoid valve for a normally open one?

A3: Usually, no. Swapping NC and NO changes what happens during power loss. Fuel, brake, and critical hydraulic circuits may depend on fail-safe normally closed behavior. Match the original function, pressure rating, electrical rating, and connector unless a qualified engineer approves the change.

 

Q4: How can I tell if my solenoid valve problem is electrical or mechanical?

A4: Start with the click test. If the valve has correct voltage and coil resistance but does not switch, the issue is often mechanical, such as a stuck plunger, worn seal, or debris in the orifice. If voltage is missing or coil resistance is open or shorted, the issue is electrical.

 

Q5: Are solenoid valves on my equipment repairable, or should I replace them?

A5: Some valves allow coil-only replacement. Others are sealed units where full replacement is faster and more reliable. If the valve body is damaged, the ports are corroded, or the internal parts are contaminated, replacement is usually best. Cross-check part numbers and specifications with your equipment manual or a trusted parts supplier like Fab Heavy Parts. For the best result, match the solenoid valve to the machine’s pressure, flow, media, voltage, and safety needs. If you are replacing valves on heavy equipment, Fab Heavy Parts can help you compare specifications and find a dependable fit for your fleet.

 

Popular Solenoid Valves at Fab Heavy Parts

1.

Solenoid Valve 6697960 Aftermarket Replacement For Bobcat Loader S100 S130 S150 S175 S185 S595 S650 T110 T140 T180 T190 T250 L85 L65 L95 Work Machine 5600 5610

Part Number: 6697960

Condition: New, aftermarket replacement

Function: Hydraulic flow switching, circuit control, and pressure regulation for loader arm, attachment, and auxiliary hydraulic system operation

Aftermarket Replacement For Bobcat Loader Models: The Solenoid Valve fits for Bobcat Loader A300, A770, S100, S130, S150, S160, S175, S185, S205, S220, S250, S300, S330, S450, S510, S530, S550, S570, S590, S595, S630, S650, S740, S750, S770, S850, T110, T140, T180, T190, T250, T300, T320, T450, T550, T590, T595, T630, T650, T740, T750, T770, T870, L65, L85, L95; Bobcat Telehandler Models: TL34.65HF, TL35.70, TL38.70HF, TL43.80HF, TL723, TL923; Bobcat Work Machine Models: 5600, 5610, UW53, UW56

 

2.

Solenoid Valve 91E72-03100 91E7203100 Fits for Mitsubishi F18C F14E F16D for Caterpillar 2C4000 Forklift

Part Numbers: 91E72-03100 (91E7203100), CT91E72-03100 (CT91E7203100), MB91E72-03100 (MB91E7203100)

Condition: New, Aftermarket

Fits Mitsubishi Forklift: The Solenoid Valve fits for Mitsubishi Forklift F14E, F16D, F18C; Fits Caterpillar Forklift: 2C4000

Package Contents: 1 x Solenoid Valve

Features: Direct replacement for seamless installation; Precision-engineered to meet or exceed factory specifications; Manufactured from high-grade materials for extended service life; Quality tested for reliable performance

 

3.

Solenoid Valve 4368974 Fits for Hitachi EX400-3 EX400-3C EX400-5 EX450H-5 EX750-5 ZX600 ZX650H ZX800 ZX850H

Part Numbers: 4368974, KDRDE5K-10/40C05-T, KDRDE5K1040C05T

Condition: New, Aftermarket

Fits Hitachi Excavator: The Solenoid Valve fits for Hitachi Excavator EX400-3, EX400-3C, EX400-5, EX400LC-3, EX400LC-3C, EX450H-5, EX450LC-5, EX750-5, EX800H-5, ZX600, ZAXIS600LC, ZX650H, ZX800, ZAXIS800, ZX850H

Package Contents: 1 x Solenoid Valve

Features: Direct replacement for seamless installation, Precision-engineered to meet or exceed factory specifications, Manufactured from high-grade materials for extended service life, Quality tested for reliable performance

 

4.

Solenoid Valve 4455991 Fits for John Deere 120C 160CLC 200CLC 225CLC for Hitachi ZAXIS230 ZAXIS240H ZAXIS120

Part Numbers: 4455991

Condition: New Aftermarket

Application: The Solenoid Valve fits for John Deere Engines: 4045HP050, 4045HP051, 6068HT053, 6068HT054, 6068HT055, 6068HT059, 6068HT064, 6068HT065, 6081HT002, 6081HT008; John Deere Excavators: 120C, 135C, 160C LC, 200CLC, 225CLC, 230CLC, 270CLC, 330CLC, 370C; Hitachi Excavators: ZAXIS120, ZAXIS135US, ZAXIS160LC, ZAXIS200F, ZAXIS200LC, ZAXIS225USLC, ZAXIS230, ZAXIS230LC, ZAXIS240, ZAXIS240H, ZAXIS240LCH, ZAXIS250F, ZAXIS270LC, ZAXIS330LC, ZAXIS350F, ZAXIS370

Package Contents: 1 x Solenoid Valve

Features: Direct replacement for seamless installation, Precision-engineered to meet or exceed factory specifications, Manufactured from high-grade materials for extended service life, Quality tested for reliable performance

 

5.

Solenoid Valve 702-21-61500 Fits for Komatsu PC240LC-10 PC290LC-10 WA500-7 WA480-8 HM300-3 HM400-3

Part Numbers: 702-21-61500, 7022161500

Condition: New, aftermarket replacement

Function: Electrically controls hydraulic fluid routing within Komatsu equipment hydraulic circuits to regulate actuator movement, implement control, and system pressure across excavator, dozer, loader, dump truck, and motor grader applications

Fits the Following Applications: The Solenoid Valve fits for Komatsu Excavator: PC128USI-10, PC138US-10, PC138US-11, PC138USLC-10, PC138USLC-11, PC240LC-10, PC240NLC-10, PC290LC-10, PC290NLC-10, PC490-10, PC490LC-10; Komatsu Loader: WA380-7, WA380Z-6, WA470-7, WA470-8, WA470-8E0, WA475-10, WA475-10E0, WA480-8, WA480-8E0, WA500-7, WA500-8, WA500-8E0; Komatsu Articulated Dump Truck: HM300-3, HM300-5, HM300-5E0, HM400-3...

Package Contents: 1 × Solenoid Valve 702-21-61500

 

6.

Hydraulic Pump Solenoid Valve YN35V00041F1 Fits for New Holland Crawler Excavator EH130 EH215 E215 Replacement

Fits Part Numbers: YN35V00041F1

Condition: New, aftermarket replacement

Function: Hydraulic pump flow and pressure control

Fits New Holland Crawler Excavators: The Hydraulic Pump Solenoid Valve fits for New Holland EH130, EH215, E215

Package Contents: 1 × Hydraulic Pump Solenoid Valve (YN35V00041F1)

 

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