Stainless 2/2-Way Solenoid Valves: Direct Acting vs Pilot Operated (SPU-03, SPX-15, SPG-06T, PG Series)
Short answer: for a stainless 2/2-way normally closed solenoid valve, first decide direct acting or pilot operated. Direct acting opens from 0 bar but has a small orifice; pilot operated gives more flow (or much higher pressure) but needs at least 0.5 bar differential pressure to open and close. Then match port size, working pressure range, seal material and coil voltage to your line. Find it by part number. Buy it with the specs in front of you.
Direct acting or pilot operated: which do I need?
- Direct acting: the coil lifts the plunger off the orifice on its own, so the valve opens with no pressure at all. Use it for gravity feeds, low-pressure water, small air lines and dosing. The trade-off is a small orifice (3 mm on the SPU-03), so flow is limited.
- Pilot operated (pilot diaphragm or pilot piston): the coil opens a small pilot passage and the line pressure does the work of opening the main seat. That allows a bigger orifice or a much higher pressure rating with the same coil size. The catch: below the minimum differential (0.5 bar on the SPX-15 and SPG-06T) it will not open or close reliably.
- Rule of thumb: if the line can be at or near 0 bar when you need the valve to switch (tank outlets, gravity, vented lines), choose direct acting. If there is always pressure behind the valve, a pilot valve gives you more flow per dollar.
Specs at a glance: stainless 2/2-way NC solenoid valves
| Product | Operation | Port / orifice | Working pressure | Seal | Coil voltages | Price |
|---|---|---|---|---|---|---|
| SPU-03 | Direct acting | G1/4 / 3 mm | 0–16 bar | NBR | 12 VDC, 24 VDC, 110 VAC, 220 VAC | $38.99 – $39.99 |
| SPX-15 | Pilot diaphragm | G1/2 / 15 mm | 0.5–15 bar (25 bar max as listed) | NBR diaphragm, up to 80 °C | 12 VDC, 24 VDC, 24 VAC, 110 VAC, 220 VAC | $75.99 – $78.99 |
| SPG-06T high pressure | Pilot operated | G1/4 female / 6 mm | 0.5–150 bar | PTFE, media -5 to 80 °C | 12 VDC, 24 VDC, 24 VAC, 110 VAC (IP65 coil) | $107.99 |
| PG Series high pressure | Not stated in the listing | G1/8 / 1 mm or G1/4 / 1.5 mm | 0–100 bar or 0–200 bar | PTFE, forged 304 body | 12 VDC, 24 VDC, 110 VAC (IP65 coil) | $174.99 – $199.99 |
Which valve fits my application?
| Application | Look at | Why |
|---|---|---|
| Water or air shut-off on a machine, lube lines, sampling, small dosing | SPU-03 | Opens from 0 bar; 3 mm orifice is enough for small flows |
| Process skid, washdown, cooling or fill line that needs more flow | SPX-15 | 15 mm orifice on G1/2 ports; needs 0.5 bar minimum differential |
| Compressed air or gas, hydraulic oil, high-pressure water, test benches up to 150 bar | SPG-06T | 6 mm orifice with a 150 bar rating and PTFE seal |
| Misting and fogging, high-pressure cleaning, pressure test benches, small injection lines up to 200 bar | PG Series | 1–1.5 mm orifice: very low flow, very high pressure; the listing states 0 bar as the bottom of its range |
Frequently asked questions
What does “normally closed” mean?
The valve is shut when the coil has no power and opens when the coil is energized. If power is lost, the line closes. All four valves above are normally closed.
Why does my pilot valve not open at low pressure?
A pilot valve uses the line pressure to lift its main diaphragm or piston. The SPX-15 and SPG-06T listings state a 0.5 bar minimum differential pressure. Below that, the valve may not open or may not close fully. For zero-pressure service, use a direct-acting valve such as the SPU-03.
NBR or PTFE seal?
The listings give NBR for the SPU-03 (air, gas, light oil, water) and the SPX-15 diaphragm (up to 80 °C), and PTFE for the two high-pressure valves (water, oil, gas; SPG-06T media -5 to 80 °C). Check the medium and temperature of your line against the listing before ordering; if your medium is not listed, the supplier does not state it.
Are the ports NPT?
No. All four use G (BSPP) parallel threads. For NPT piping, use a G-to-NPT adapter and a sealing washer or bonded seal, not just thread tape.
Which coil voltage should I pick?
Match the coil to the output that drives it: 24 VDC is the usual choice for a PLC digital output or relay in a control panel; 110 VAC or 220 VAC for line-powered circuits. Each product page lists the voltages it is offered in, and the price updates for each option.
Can I use these valves on flammable gas or in a hazardous (classified) area?
The listings do not state any hazardous-area or explosion-proof rating. Do not install them in classified locations, and do not use them as a safety shut-off. Follow your site’s rules for gas service.
Can I watch line pressure remotely while the valve cycles?
A 4-20 mA pressure transmitter on the line can go through a Modbus I/O module or gateway to AutomationBotX Cloud: live pressure, trend chart and alarm rules in the app. It is read-only monitoring: it never sends commands, so it does not open or close the valve, and it is not a safety system. The first 10 machines are free, no card needed. How the signal gets from the sensor to your phone.
Need several units?
Ask for a written volume quote on our wholesale page. More valves and field equipment: oil and gas automation.
Free US shipping on every order. Specs above come from the product listings; if a value you need is not listed, it is not stated by the supplier. Prices checked on November 11, 2026 and may change; the product page shows the current price.