Written by: A.J. Piskor
One of the key pieces of any combustion system are the safety shutoff valves. Their job is important, stop the fuel from entering the system when requested or when a fault is detected. With the harsh operating environments and demanding cycling that these valves sometimes go through, internal components have been known to fail. Not only does this bring the shutoff valve down (to a safe position), but it also brings down the combustion system with it.
Maxon shutoff valves are known for their performance, reliability, and durability. In the rare case that one of their automatic reset gas valves (Series 5000/SMA11 or 5000CP/CMA11 for normally closed models, series STOA/SMA21 or STOACP/CMA21 for normally open models) fails to perform, it’s possible that one of the internal components could have gone bad. Each Maxon automatic reset shutoff valve comes with three critical electrical components (solenoid, motor, position switch) that need to work together for the valve to operate properly. By listening to the valve cycle to its energized state, you can detect if any of these critical electrical components needs to be replaced.
Here is the sound of a properly working Maxon shutoff valve:
At the beginning of the clip, you can hear a sharp, snapping sound. This is the sound of the solenoid plunger engaging with the solenoid coil. You can also hear the hum of the motor at the same time. After a few seconds, the pitch of the motor changes, as the motor is now pushing the stem and disc of the valve against the return spring into the valve body. Once the stem and disc reached the proper position within the valve body, an internal position switch shuts off power to the motor. The solenoid remains on after the motor is off, which is the buzzing sound towards the end of the clip.
Now that we know what a normal sequence sounds like, let’s try one with a failed electrical component:
In this clip, we don’t hear the snapping sound at the beginning like we did in the previous clip. We only hear the motor going, and the pitch of the motor does not change. In this case, the solenoid is not working. When the solenoid is working and engaged, it positions a pedestal underneath a rocker arm. The rocker arm is supposed to translate the work from the motor to the stem and disc, which causes the motor’s pitch to change. Without the solenoid functioning, the motor continues to cycle without changing pitch. Since the valve and disc assembly do not travel in this scenario, the position switch is never engaged and therefore, power is continually applied to the motor.
Let’s listen to another clip, this time with a different failed electrical component:
In this clip, you hear the snapping sound of the solenoid engaging, but the buzzing we hear sounds different. What’s missing here is the sound of the motor. Although this clip mimics the sound of a failed motor within an automatic reset shutoff valve, it also mimics the sound of a properly functioning manual reset shutoff valve (Series 808/SMM11 or 808CP/CMM11 for normally closed models, series STOM/SMM21 or STOMCP/CMM21 for normally open models), since those valves have a manual handle in place of a motor.
The last critical component I mentioned was the internal position switch. Here’s what it sounds like when the switch has failed:
We hear all the familiar sounds with the properly working valve at the beginning of this clip with the solenoid engaging and the motor coming on and changing pitch. Instead of hearing the motor shut-off and hearing just the buzz of the solenoid, we hear a couple of knocking sounds followed by the sound of the motor overcoming the return spring again. The knocking sounds are when the valve overshoots the energized state and cycles back to the neutral state before immediately cycling again. You can also diagnose this problem by looking at the visual indication window on the valve cycle between states.
DISCLAIMER: If you are testing a valve installed within a line that you suspect is not functioning properly, you MUST make sure that the gas supply entering the fuel train is manually closed and locked-out. If the valve in question is failing in the energized state, shutdown your system IMMEDIATELY and remove the valve from service.
Learn more about Maxon Shutoff Valves
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A.J. Piskor joined Lesman as the combustion and controls specialist in early 2014 after spending nearly 10 years with our manufacturer partner, Maxon, as a technical sales engineer. Prior to that, he served as a technical sales engineer for a specialty chemical company. He also holds a Bachelor’s degree in aerospace engineering and mechanics from the University of Minnesota.
Want to learn more about combustion control systems? Call Lesman at 800-953-7626 and ask to speak to A.J.
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