For safety reasons, the PRIMUS door control system requires the operating technician to press the door button until the door is closed. The door control system has to know that the door is fully closed in order to stay closed. If not, the door will reverse and open. Two door-closed switches have to be “made”, or closed, for the door to stay closed.

Each power door has two switches to detect when the door is fully closed. Door switches send 5 VDC to the input relay when both switches are closed. Wired in series, one switch is a mechanical switch that is easy to locate on the sterilizer. The other switch is a magnetic reed switch that closes when exposed to the magnetic field of a permanent magnet in the piston of the pneumatic door cylinder. The magnetic reed switch on the door cylinder position is adjustable.

Another magnetic reed switch is on the other end of
the cylinder to detect when the door is fully open.


Look at the DOOR SW. CLOSED relay to determine if it lights up when the door is fully closed. If it does not light, then one of the following is happening:

  • One of the two switches is not closing (Most likely)
  • There is a problem with the wiring (Not very likely)
  • The input relay is bad (Unlikely)

Check the adjustment of the switches:

  • The mechanical switch is easy to check visually. It needs to be set so it has a small amount of “dead band” after the switch is made. Adjust it so it makes with a bit of tolerance or allowance.
  • The magnetic reed switch position is set to a position that when the door is fully closed it is exposed to the middle of the magnetic field of the piston magnet.

The relay’s LED should light when both switches are closed. Wire 10 supplies 5vdc to one switch, and when it is closed, sends 5 VDC to the next switch, and when it is closed, then on to the input relay in reference to ground, (connection points 21 and 22 at the relay).

To determine if it is a control input problem, look at the relays. If the input relay does not get 5 VDC, the input relay will not light up. You will then see (if in OPER mode), the OPEN DOOR output relay in slot 18 lights up, energizing the air valve to open the door.

As an unlikely possibility if the control system is working properly, uncontrolled air could be leaking through the air valve to continuously push on the piston. Check this by disconnecting the airline to the cylinder to see if air is coming out when the air valve is not actuated.

Have a question or having difficulties? Talk to Dave Schall, our PRIMUS sterilizer expert who is here to assist you anytime at 877.679.7800 extension 1212 or email at dschall@spire-is.com.

Visit us at spire-is.com

Back to Blog