Solenoid Valve vs. Relay: 4 Comparison Points — Role, Structure and Action, Electrical and Load, Selection and Pairing

A solenoid valve uses the force of a coil to open or close a fluid path; a relay uses the force of a coil to switch the contacts of a circuit. Both act when the coil is energized, and the sources say their coils and drive circuits are similar, but one manages a fluid and the other a circuit. The difference is “does it control a fluid or a circuit”, and there are four places to look: role, structure and action, electrical and load, and selection and pairing.

In this article, “solenoid valve” means a valve controlling gas or liquid, and “relay” means an electromechanical relay with mechanical contacts. Solid-state relays, contactors and automotive solenoid switches are not compared.

• Point 1 | Role: one opens or blocks a fluid, the other makes or breaks a circuit.
• Point 2 | Structure and action: plunger, valve body and pilot, against armature and contacts.
• Point 3 | Electrical and load: coil voltage, inrush current and back EMF.
• Point 4 | Selection and pairing: what to check for each, and how to check the load.

Sources are listed in the notes at the end. This is a selection overview, not circuit design, and it does not replace the maker’s data sheet; coil voltage, pressure and load depend on your site and the maker’s data. For each product’s own selection steps, see How to choose a solenoid valve and How to choose a relay; this article covers only the differences. This is the general case; individual cases vary.

Point 1 | Role: one opens or blocks a fluid, the other makes or breaks a circuit

How to look at it:

• First write down whether you are controlling a gas or liquid path, or an electrical circuit.
• To open or block a fluid, or switch flow direction, look at a solenoid valve.
• To use one signal to make or break another circuit, look at a relay.
• “Open” and “closed” may mean opposite things for the two.

What public sources say:

• An embedded-computing site article (23 Sep 2021, by a freelance technical writer; source 2): a solenoid valve can be seen as the relay concept applied to fluids; simple types only open and close, others switch flow direction, some use two coils. By analogy, an open valve lets fluid through while a closed circuit switch lets current through, so “open” and “closed” mean opposite things.
• A blog post by an industrial-parts distributor (22 Jul 2026, by an assistant product manager on its fluid-power team; seller’s view; source 4): the valve does not push fluid; it only blocks or opens an orifice.
• A blog post by an electrical-parts distributor (published 15 Apr 2026, updated 23 Apr; no personal byline; seller’s view; source 1): a relay switches lower-current signals; its output is only the on/off state of a circuit and it cannot push or pull mechanical parts.

Point 2 | Structure and action: plunger, valve body and pilot, against armature and contacts

How to look at it:

• First write down whether you need a fluid path or a number of contact sets.
• For a solenoid valve, check direct-acting or pilot-operated, number of ports, and whether it is closed or open when de-energized.
• For a relay, check contact configuration: normally open, normally closed or changeover.
• Most general types have spring return and go back to their rest position when de-energized (sources 4, 5).

What public sources say:

• An article in a valve-industry association publication (8 Apr 2019; author works for a solenoid valve maker; source 3): the coil is the electrical part and the valve body the mechanical part controlling flow. In a direct-acting valve the coil’s field pulls the plunger off the orifice so the medium flows from inlet to outlet, with few moving parts. In a pilot-operated valve the coil still lifts the core, but through pilot and bleed orifices part of the inlet line pressure lifts a diaphragm or piston.
• The industrial-parts distributor post (source 4): a solenoid valve is a valve body with a coil above it; the coil surrounds a ferromagnetic plunger and return spring. Normally closed means the spring closes it when de-energized; normally open means the spring opens it.
• An FAQ article on an electronics site (13 Nov 2017, with byline; source 5): a relay has a coil and armature; the armature moves to make or break contacts and a spring returns it. Coil and contact circuits are electrically isolated; contacts can be normally open, normally closed or multiple sets and can switch AC or DC.
• The embedded-computing article (source 2): a relay’s action can be seen and heard, which helps troubleshooting.

Point 3 | Electrical and load: coil voltage, inrush current and back EMF

How to look at it:

• First write down the voltage and current of the control signal, and the type of load being switched.
• Both coils need their specified voltage.
• Loads such as solenoids and motors draw several times their steady-state current at switch-on.
• Switching off an inductive load can produce a high back EMF, so add protection.

What public sources say:

• The embedded-computing article (source 2): a solenoid needs far more current and voltage than a microcontroller pin can supply, so a transistor or driver chip is usually needed. A relay is much slower than a transistor but gives electrical isolation and can switch AC or DC.
• A relay maker’s technical document (no date on the page, metadata July 2014, no byline; maker’s view; source 6): apply only the rated voltage to the coil; AC coils within +10% to −15% of rating, DC coils recommended within ±5%. Catalog control capacities are for resistive loads only. Inrush current is several times steady state: 10 to 20 times for solenoids, 5 to 10 times for motors. A DC relay switching an inductive load can produce a back EMF of hundreds to thousands of volts, which a diode or RC snubber can absorb.
• The FAQ article (source 5): holding current is much lower than pull-in current, about half.

Point 4 | Selection and pairing: what to check for each, and how to check the load

How to look at it:

• First write down fluid pressure and flow, circuit voltage and load, and how many operations you need.
• For a solenoid valve: port size, flow, pressure range and default state.
• For a relay: coil rating, contact rating, and whether the load is AC or DC.
• Check relay contacts against the load’s inrush current; a solenoid valve coil is itself a load.

What public sources say:

• The association publication (source 3): solenoid valve selection looks at flow coefficient, minimum and maximum line pressure, power use and total cost of ownership. Direct-acting valves have a minimum pressure differential of zero and most can work down to vacuum, but the orifice must be small. Pilot-operated valves offer larger ports and higher flow coefficients, at the cost of more parts, a lower maximum pressure and usually a higher unit cost.
• The industrial-parts distributor post (source 4): products can be filtered by valve type, port size, working pressure, coil voltage and medium; its comparison table also lists default state and port count; typical switching time is 10 to 100 ms.
• The embedded-computing article (source 2): a solenoid reacts quickly but has little force; for more force a solenoid valve can drive an air cylinder, at the cost of more complex piping and possible air leaks.
• The electrical-parts distributor post (source 1): a relay acts in 5 to 50 ms, with no source given.
• The FAQ article (source 5): relay selection looks at coil rating, contact configuration, contact current and voltage ratings, and whether the load is AC or DC. Arcing on opening damages contact plating. Operation takes tens of milliseconds and can exceed a million cycles within design limits. Drawbacks: slow, subject to wear, larger and more costly than a solid-state relay.
• The relay maker’s document (source 6): rated life is only a reference; inrush current and running close to rating both shorten life. Large AC types act in 7 to 16 ms.

Comparison table: four points at a glance

Sources: 1 to 6. These are what the sources say, not selection thresholds.

How to choose: when to look at a solenoid valve, when at a relay

• Look at a solenoid valve when: you need to open or block a gas or liquid, or switch flow direction. Decide first on port count, direct-acting or pilot, flow and pressure range, and the de-energized default state (sources 2, 3, 4).
• Look at a relay when: you need a smaller signal to make or break another circuit, or you need electrical isolation. Decide first on coil rating, contact configuration and rating, and load type (sources 1, 2, 5, 6).
• Points to watch: source 6 lists solenoids as loads with very high inrush; relay contacts must be checked against such loads, not just the catalog resistive rating. Source 1’s “solenoid” means devices that produce mechanical motion, including starter motors, winches and hydraulic valves, which is not quite the same as the solenoid valve in this article; only its statements about relays are used here (sources 1, 6).
• Near the boundary: the sources give no line for “use a relay or drive it directly with a driver circuit”, and their inrush ratios and operating times differ because they discuss different objects and conditions. Go by your actual load and the maker’s data (sources 2, 5, 6).

These are statements from public sources, not a conclusion for your site; which to use, and at what rating, depends on your fluid, circuit and load.

How JIAHON can help

The list below uses only product names and page titles from JIAHON product pages. For number of ways, direct-acting or pilot, port size, coil voltage and fittings (solenoid valve side), and relay type, contacts, coil or control voltage and ratings (relay side), please ask.

Solenoid valve side: solenoid valves, pneumatic solenoid valves, solenoid valves, pilot valves and regulators.

Relay side: auxiliary relays, general-purpose and timer relays, miniature relays, solid-state relays, compact plug-in relays, PCB power relays, phase-sequence relays.

To match a type, prepare six items: whether you are controlling a fluid or a circuit; fluid type, pressure and flow; circuit voltage, current and load type; control signal voltage and source; operating frequency and expected life; the model you use now and the problem you see. Contact JIAHON or email [email protected].

Notes: sources and limitations

Where the maker’s data sheet, your site’s load or your purchasing requirements differ from this article, they take precedence.

• What was seen: six sources: two from sellers, two from makers or maker staff, two technical-site articles. No neutral-body document and no standard text was read; sources 5 and 6 are older, sources 1 and 4 are sellers, and the figures carry no test standard.
• What was not seen: no neutral comparison of solenoid valves and relays; no line for “relay or direct driver circuit”. Source 3 is inconsistent about pilot-valve power use, so that point is not cited.
• Where sources differ: operating times (relay 5–50 ms in source 1, valve 10–100 ms in source 4, relay tens of ms in source 5, large AC relay 7–16 ms in source 6) roughly overlap but use different definitions; they are listed side by side.
• Single-source points: the “open/closed” reversal and valve-as-relay analogy (source 2); force and cylinder trade-off (source 2); zero minimum differential and pilot trade-offs (source 3); 10–100 ms valve switching (source 4); holding current about half, over a million cycles (source 5); coil voltage tolerance, inrush ratios, back EMF, rated life as reference (source 6); 5–50 ms relay action (source 1).
• Translation: the sources are in English; statements here are paraphrased, not quoted.
• This article’s own work: the “How to look at it” points and the “How to choose” grouping are an arrangement of the sources, not their wording.
• Products: “How JIAHON can help” uses only product names and page titles; it does not cite models or ratings. Please confirm specs with sales.

This is a general overview, not circuit design, and not an endorsement of any solenoid valve or relay maker, brand, supplier or service provider. Go by the maker’s data sheet, your site’s load and purchasing requirements, and your own evaluation. This is the general case; individual cases vary.