SMC JSXR Water Hammer Relief 2-Port Solenoid Valve: How It Works and When to Use It
2026-11-09If closing a water solenoid valve makes the pipe bang, the gauge needle jump and the line shake, you are looking at water hammer. A standard pilot-operated 2-port valve shuts quickly; on a long run of pipe, the moving column of water is stopped almost instantly and the pressure spike can be several times the line pressure. Over time that hurts valves, fittings and whatever sits downstream. SMC added the JSXR water hammer relief series to its JSX 2-port solenoid valve family to tackle exactly this by closing the main valve more slowly. This guide sticks to what SMC publishes on its new-products page and in the JSX/JSXR catalogue, so you can decide whether JSXR suits your line and what to check before you order.
The short answer
JSXR is a normally closed (N.C.), pilot-operated diaphragm 2-port solenoid valve for water only (1 to 60 °C). Max. system pressure is 1 MPa, the minimum operating pressure differential is 0.04 MPa, port sizes run from 1/2 to 2, and orifice diameters from 20 to 50 mm. A two-stage supply into the valve’s pressure chamber slows the final part of the closing stroke, which relieves water hammer. SMC’s own example: on 30 m of SGP steel pipe with the same bore as the valve and 0.5 MPa initial pressure, a JSXR51/61 produces a peak of about 1.1 MPa, against 4.0 to 7.0 MPa for a general-purpose solenoid valve. If your medium is air, steam or oil, or your line has almost no pressure differential, look elsewhere.
Where water hammer comes from
Water barely compresses. When a valve cuts off flowing water fast, the kinetic energy of the water column turns into a pressure wave that travels back and forth along the pipe: you hear a bang, feel vibration and see a pressure spike. Longer pipes, higher flow velocity and faster closing all make it worse. SMC’s JSX precautions say it plainly: an impact from rapid pressure fluctuation such as water hammer may damage the valve, so fit relief equipment such as an accumulator or use an SMC water hammer relief valve.
How JSXR closes slowly
From the construction notes in SMC’s catalogue:
- Opening: the coil is energised, the armature is pulled in, the pilot valve opens, pressure in the pressure action chamber drops and the main valve opens.
- Closing: the coil is de-energised, the pilot valve closes, chamber pressure rises and the main valve closes.
- Water hammer relief: the chamber is fed through two supply orifices (D and E). E has a check-valve mechanism, and supply is controlled in two stages as the diaphragm assembly moves. Once the main valve is nearly closed, E is blocked, so the last part of the stroke is slow and the pressure spike is reduced.
In other words, the damping happens inside the valve rather than in an add-on device. It also means response time is not a fixed figure: SMC’s operation manual lists it as variable, depending on pressure, voltage fluctuation and piping conditions.
Official specifications
| Item | JSXR series |
|---|---|
| Construction / type | Pilot-operated diaphragm; normally closed (N.C.) |
| Fluid | Water, 1 to 60 °C |
| Body material | Bronze |
| Withstand / max. system pressure | 2 MPa / 1 MPa |
| Operating pressure differential | Min. 0.04 MPa, max. 1.0 MPa |
| Ambient temperature | −20 to 60 °C |
| Valve / external leakage (water) | 1 cm³/min or less / 2 cm³/min or less |
| Mounting orientation | Unrestricted (per catalogue) |
| Enclosure | IP67 (IP65 for DIN terminal and conduit terminal) |
| Seal material | NBR or FKM |
| Rated voltage | AC 24, 48, 100, 110, 120, 200, 220, 230, 240 V; DC 12, 24 V |
| Power | Size 50: 8 VA AC / 6 W DC; size 60: 9.5 VA / 8 W; sizes 70 to 90: 16 VA / 13 W |
| Standards | CE / UKCA |
Sizes, flow and weight
| Size | Port | Orifice | Kv | Cv (conv.) | Model | Weight (grommet) |
|---|---|---|---|---|---|---|
| 50 | 1/2 | 20 mm | 5.7 | 6.5 | JSXR51-B□04 | 1320 g |
| 50 | 3/4 | 20 mm | 6.4 | 7.5 | JSXR51-B□06 | 1320 g |
| 60 | 1 | 25 mm | 10.3 | 12.0 | JSXR61-B□10 | 1800 g |
| 70 | 1 1/4 | 35 mm | 18.9 | 22.0 | JSXR71-B□12 | 2970 g |
| 80 | 1 1/2 | 40 mm | 25.7 | 30.0 | JSXR81-B□14 | 3770 g |
| 90 | 2 | 50 mm | 42.8 | 48.0 | JSXR91-B□20 | 4670 g |
SMC notes that flow characteristics of this product vary. Conduit, DIN terminal, M12 and conduit terminal versions add weight; see the catalogue.
How much does it help? SMC’s two examples
| Model | Condition (SMC catalogue) | JSXR peak pressure | General-purpose valve |
|---|---|---|---|
| JSXR51 / 61 | 30 m SGP pipe, same bore, 0.5 MPa initial | about 1.1 MPa | 4.0 to 7.0 MPa |
| JSXR71 / 81 / 91 | 30 m SGP pipe, same bore, 0.5 MPa initial | about 0.8 MPa | 2.0 to 4.0 MPa |
These are worked examples read from SMC’s characteristic curves. Your result depends on pipe length, pipe material, flow velocity and initial pressure, so check the curves against your own line.
Reading the part number
Using SMC’s example JSXR51-BN04R-5GD (always confirm against the catalogue How to Order):
- JSXR: water hammer relief, pilot-operated 2-port solenoid valve
- 5: size (5 to 9 = sizes 50 to 90)
- 1: valve type, N.C.
- B: body material, bronze
- N: seal (N = NBR, F = FKM)
- 04: port size (04 = 1/2, 06 = 3/4, 10 = 1, 12 = 1 1/4, 14 = 1 1/2, 20 = 2)
- R: thread (R = Rc, N = NPT, F = G)
- 5: rated voltage (e.g. 5 = 24 VDC, 6 = 12 VDC, 3 = 120 (110) VAC, 4 = 220 VAC, J = 230 VAC)
- G: electrical entry (G grommet; GS grommet with surge suppressor; CS conduit; DS/DZ/DN DIN terminal; WN M12 connector; TS conduit terminal)
- D: oil-free option (blank = none)
Note that the M12 connector version (WN) ships without a cable; order it separately.
When JSXR makes sense
- The medium is water, the pipe run is long, and closing the valve causes banging, vibration or pressure spikes.
- Pressure-sensitive equipment, instruments or hoses sit downstream.
- Port size is between 1/2 and 2 and line pressure stays at or below 1 MPa.
- You can keep at least 0.04 MPa across the valve.
When to choose something else
- Not water: for air, steam, heated water, oil or vacuum, use other JSX models. The JSXR catalogue lists water only.
- Near-zero differential: pilot operation needs at least 0.04 MPa. For zero or low differential, SMC offers the JSXZ zero differential pressure series.
- Fast shut-off required: slow closing is the whole point of JSXR, so a process that needs a fast cut-off needs a different approach.
- Possible back pressure: SMC’s manual warns that an N.C. valve will not block flow if outlet pressure exceeds inlet pressure; add a check valve or similar if back pressure can occur.
Pre-order checklist
| Check | What to confirm |
|---|---|
| Fluid and temperature | Water, within 1 to 60 °C |
| Pressure | Max. ≤ 1 MPa; differential ≥ 0.04 MPa |
| Size and flow | Size by Kv/Cv, not by port size alone |
| Thread | Rc, NPT or G to match your fittings |
| Seal | NBR or FKM for your water quality and environment |
| Voltage and wiring | Voltage code; grommet, DIN, M12 or conduit; M12 cable ordered separately |
| Environment | Outdoors or constant spray: add water protection as the catalogue advises (DIN terminal is IP65) |
| Water hammer estimate | Pipe length, material and initial pressure checked against SMC’s curves |
For valve basics, see our pneumatic directional control valve selection guide, or browse the SMC product category.
Talk to us
Send us your medium, line pressure and port size, pipe length, voltage and preferred electrical entry at doskee@dustry.ltd. We will help you list the points to confirm with SMC.
FAQ
Can JSXR be used on compressed air or steam?
No. SMC lists water as the only applicable fluid for JSXR. Use other JSX models for air, steam or oil.
Does JSXR eliminate water hammer completely?
SMC describes it as relief. Slower closing lowers the peak pressure; how much depends on pipe length, initial pressure and other conditions. Use the catalogue curves to estimate.
Why does it need a pressure differential?
JSXR is a pilot-operated diaphragm valve that uses line pressure to move the main valve, and SMC specifies a minimum operating differential of 0.04 MPa. Consider the JSXZ zero differential series if you cannot guarantee that.
Any mounting orientation limits?
The catalogue’s common specifications list mounting orientation as unrestricted. Follow the operation manual supplied with the valve for installation details.
Can it go outdoors?
The enclosure is IP67 (IP65 for DIN terminal and conduit terminal). SMC warns that water getting into the product can cause malfunction, so add protection outdoors or under constant spray.
Sources: SMC new products list (JSX/JSX□ series, JSXR added Oct 2025); SMC JSX/JSX□ series catalogue (JSXR on pp. 63–68); SMC JSXR operation manual.