Choosing a Solenoid Valve for Diesel, Fuel Oil and Heating Oil
Solenoid valves are widely used to start, stop and safely isolate liquid fuels in oil-fired burners, standby generators, boiler rooms, farm bulk tanks and plant machinery. Fuel oil is unforgiving of the wrong specification: an incompatible seal will swell and leak, an undersized valve will starve the burner, and a valve that fails open creates a genuine fire and spillage risk. This guide walks through the key decisions so you can specify a fuel valve that is safe, compatible and correctly sized for your line.
Know your fuel grade first
"Fuel oil" covers a family of petroleum distillates with quite different viscosities and cold-flow behaviour, and the grade you are handling drives seal, sizing and heating decisions. Typical UK applications include gas oil (red diesel / 35-second oil) for burners and mobile plant, kerosene (28-second oil) for domestic and light commercial heating, road diesel and biodiesel blends (B7, B20 and higher) for generators and vehicles, and heavier fuel oils that are viscous at ambient temperature and usually need trace heating. The heavier and colder the oil, the more viscosity works against you, so the fuel grade should be the first thing you pin down.
Seal material is the decision that fails valves
The single most common cause of a leaking fuel valve is the wrong elastomer. Petroleum distillates attack some rubbers and are perfectly compatible with others, so this choice is not optional. As a rule of thumb, nitrile (NBR) is the standard, cost-effective seal for mineral diesel, kerosene and gas oil; FKM (Viton) is the premium choice for higher temperatures, aromatic content and biodiesel blends; and EPDM must be avoided entirely, because it swells and degrades rapidly in hydrocarbon fuels. Always confirm the specific fuel and any additives against the manufacturer's data before ordering, especially with high biodiesel blends, which can be more aggressive to seals than mineral diesel.
| Seal material | Diesel / gas oil / kerosene | Biodiesel blends | Notes |
|---|---|---|---|
| NBR (Nitrile) | Recommended | Low blends only (check) | Standard, economical choice for mineral fuel oils |
| FKM (Viton) | Recommended | Recommended | Best for higher temperatures and higher biodiesel content |
| EPDM | Not suitable | Not suitable | Swells badly in petroleum fuels — never use |
If you are ever unsure, our seal materials guide and free chemical compatibility guide let you cross-check the media against each elastomer before you commit.
Body material
Brass is the usual body material for diesel and heating oil and offers good compatibility with a low cost. Stainless steel is chosen where corrosion resistance matters — marine environments, salt-laden air, or where the valve must resist external weathering as well as the fuel inside. Aluminium bodies appear on some burner valves to save weight. For most land-based oil-fired heating and generator duties, a brass valve with the correct seal is entirely appropriate; step up to stainless where the surroundings, not the fuel, demand it.
Normally closed for fail-safe shut-off
Fuel lines should almost always use a normally closed (NC) valve, so that the valve is held open only while energised and springs shut the instant power is removed. This gives you inherent fail-safe behaviour: a power cut, a blown fuse or a burner lockout all default the fuel supply to OFF. Normally open valves have their place in venting or recirculation duties, but for the main fuel feed to a burner or engine, normally closed is the safe default and is what most burner safety interlocks expect.
Direct-acting versus pilot-operated — mind the pressure
This is where fuel systems catch people out. Pilot-operated (servo-assisted) valves rely on a minimum pressure difference across the valve to open and stay open. Many fuel arrangements — gravity-fed tanks, suction-side plumbing before a pump, or low-pressure lift feeds — simply do not provide that differential, and a pilot-operated valve will refuse to open or will chatter. For low-flow, low-pressure and gravity-fed fuel lines, choose a direct-acting valve, which opens from zero pressure differential. Reserve pilot-operated valves for pumped lines that reliably maintain the manufacturer's stated minimum operating pressure differential.
Sizing, viscosity and cold weather
Size the valve on flow and pressure drop, not on the pipe thread. A valve with an orifice that is too small will throttle the fuel and starve the burner at high fire; one that is generously sized keeps pressure drop low. Viscosity matters more with fuel oil than with water: kerosene is thin, but gas oil and heavier grades thicken considerably as temperature falls, which slows response and increases pressure loss. Allow for worst-case cold-start conditions, and remember that genuinely heavy fuel oils normally require trace heating to reach a pumpable, valve-friendly viscosity. Our note on media viscosity explains how thicker fluids affect valve selection.
Protect the seat — always fit a filter
Fuel picks up rust, sludge and tank sediment, and the tiniest particle trapped on a valve seat causes weeping and eventual failure to seal. Fit an upstream strainer or filter sized for the line, and keep it maintained. This one inexpensive precaution prevents a large share of the fuel-valve faults we see. If a valve does start passing or sticking, our fault-finding guide helps isolate whether the cause is debris, a worn seat or a coil problem.
Hazardous areas and electrical points
Fuel storage and dispensing areas may be classified as hazardous (potentially explosive atmosphere) zones, in which case an ATEX-certified valve and coil are required rather than a standard industrial unit. Even outside classified zones, specify a coil voltage that matches your control system (commonly 230V AC or 24V DC), a suitable DIN connector, and an IP rating appropriate to a boiler room or outdoor tank installation. If your duty overlaps with gaseous fuels, our gas valve guide covers the additional safety approvals that apply to gas rather than liquid fuels.
A quick specification checklist
Before you order, confirm: the exact fuel grade and any biodiesel content; an NBR or FKM seal (never EPDM); a body material suited to the surroundings; normally closed action for fail-safe shut-off; direct-acting where pressure is low or gravity-fed; an orifice sized for cold, worst-case flow; an upstream filter; and the correct coil voltage, connector, IP and any ATEX requirement. Getting these right the first time avoids leaks, burner faults and unplanned downtime.
Need help specifying?
If you would like a shortlist matched to your fuel, flow and pressure, browse our range of fuel solenoid valves or work through the general how to choose a solenoid valve guide. If anything is unclear — particularly around seal compatibility or minimum operating pressure — contact our technical team with your fuel type and line details before you order, and we will help you get the specification right first time.