3/2-way load/unload solenoid (generic)

The pilot valve that sends control air to the inlet valve and blowdown line. Energise to load, de-energise to unload on most machines.

Also called: loading solenoid · 1SV · SV1 · capacity control solenoid

Normally closed P→A. Most OEMs wire it energised-to-load so a control failure or power loss drops the machine to unloaded/safe. A few older CompAir/Boge designs invert this — verify on the schematic before condemning a coil.

How it works

A 3/2-way pilot solenoid ported P (control air supply, taken downstream of the separator or from the sump), A (to the inlet valve actuator) and R (exhaust/vent). Energised: P→A, the inlet valve opens and the machine loads. De-energised: A→R, the actuator vents, the inlet valve spring-closes and the blowdown vents the sump.

Coil resistance (typical, cold DC)

Typical values for the stated wattage class. Always compare against the coil tag. Open circuit = burnt winding; near 0 Ω = shorted turns.

Specifications

Body port size

1/8" – 1/4" NPT / G

Orifice

1.6 – 3.0 mm

Working pressure

0 – 150 PSIG (10 bar) pilot

Media temp

-10 to 80 °C (14 – 176 °F)

Duty

100 % ED, continuous

Enclosure

IP65 with moulded DIN 43650-A connector

Parts you can order

• ASCO (Emerson)

  Series 210 general service

  8210G002

  $95 – $210
• ASCO (Emerson)

  Red-Hat replacement coil

  238610-032-D (120 V/60 Hz)

  $35 – $90
• ASCO (Emerson)

  Series 8320 3-way universal

  8320G174

  $130 – $300
• ASCO (Emerson)

  Red-Hat II replacement coil

  238610-032-D (120/60)

  $45 – $110
• Parker (Skinner)

  7000 series 2-way NC

  71216SN2MN00N0C111C2

  $80 – $180
• Bürkert

  Type 6013 2/2-way

  6013 (configure by orifice/voltage)

  $110 – $240
• Norgren

  Series 83 direct solenoid

  8320300.9101.02400

  $95 – $210
• SMC

  VX21 2-port direct-operated

  VX2120-02-5DZ1

  $70 – $150
• Humphrey

  410 series 3-way poppet

  410 (voltage suffix)

  $90 – $190

Field test procedure

1. Lock out and bleed sump pressure to 0 before removing any pilot line.
2. Unplug the DIN connector and ohm the coil pin-to-pin. Compare with the coil's own voltage/wattage tag using the table above.
3. Open coil (OL) = burnt winding. Near 0 Ω = shorted turns. Both mean replace the coil, not the valve body.
4. Megger coil-to-body at 500 V: expect > 20 MΩ. Under 1 MΩ means moisture ingress — the DIN gasket is the usual culprit.
5. With power on and the machine commanded to load, measure voltage at the coil. Voltage present + no click = failed coil or a stuck armature.
6. Voltage present, coil good, still no load: pull the valve and check for varnish on the armature and a plugged 1.6 mm orifice.

Symptoms & probable causes

• Machine never loads
  No coil voltage (controller output, fuse, or relay), open coil, or plugged pilot orifice.
• Machine loads but will not unload
  Armature stuck open on varnish, or exhaust port R plugged so the actuator cannot vent.
• Continuous air leak from the vent port
  Seat debris or a swollen elastomer seal. Rebuild kit or replace.
• Coil burns repeatedly
  Wrong voltage coil, AC coil held off its seat (never fully pulls in), or > 10 % over-voltage.
• Loads for a second then dumps
  Control air supply restricted, or the actuator diaphragm is leaking down.