Getting your compressor to start smoothly usually involves checking the control devices inc unloader valve to see if it's venting pressure correctly. If you've ever flipped the switch on your air compressor only to hear a pathetic hum followed by a tripped circuit breaker, you know exactly how frustrating it can be. Most people think their motor is dying or the pump has seized up, but more often than not, it's just a tiny valve that isn't doing its job.
The unloader valve is one of those components that you don't really think about until it fails. It's a small part, but it plays a massive role in how your machine operates. Essentially, its job is to get rid of the "head pressure"—the trapped air sitting on top of the compressor piston—so the motor doesn't have to fight against that pressure the next time it tries to turn over. When you have a control devices inc unloader valve that's gunked up or worn out, that pressure stays trapped, and your motor simply can't push against it.
What's Actually Happening Inside?
To understand why your compressor is acting up, you have to look at what the valve does during a normal cycle. When your tank reaches its "cut-out" pressure (the point where it's full and the motor stops), the pressure switch sends a signal to the unloader valve to open up. You'll hear a distinct "psshhh" sound. That's the sound of success. It's the air escaping from the discharge line.
If you don't hear that sound, or if you hear a constant, never-ending hiss, you've got a problem. Control Devices Inc. makes a lot of these valves for major compressor brands, so they're built well, but they aren't immortal. Over time, heat, moisture, and tiny bits of debris from the pump can settle inside the valve body. Since these valves rely on very tight tolerances and small springs, it doesn't take much to throw them off balance.
Identifying the Symptoms of a Bad Valve
How do you know for sure that it's the control devices inc unloader valve and not something else? There are a few telltale signs that point directly to this part.
First, there's the "stutter start." This happens when the motor tries to turn, moves a fraction of an inch, and then stops or blows a fuse. This is almost always due to trapped head pressure. If you manually bleed the air out of the tank and the compressor starts fine, but then fails to restart once it's partially full, your unloader isn't venting.
Second, watch out for the "endless hiss." If the compressor is running and you hear air leaking from the pressure switch area, or if it keeps hissing long after the motor has shut off, the valve is stuck open. This is annoying because it makes your compressor run way more often than it should, wearing out the pump and wasting electricity. It's like trying to fill a bucket with a hole in the bottom.
Troubleshooting the Control Devices Inc Unloader Valve
Before you run out and buy a brand-new part, it's worth taking a look to see if you can save the one you have. Most of these valves are pretty simple to take apart. However—and I can't stress this enough—unplug the compressor and drain the tank completely before you touch anything. Working on a pressurized system is a great way to get a face full of metal parts.
Once the system is dead, locate the valve. On many portable units, the control devices inc unloader valve is integrated directly into the pressure switch. You'll see a small copper or plastic line running from the pump to the switch; that's your target.
- Check the line: Sometimes the unloader line itself is cracked or the fittings are loose. If air is leaking from the tube rather than the valve, a quick tighten or a new piece of tubing might fix it.
- Inspect the piston: If you pull the valve apart, you'll see a tiny piston and a spring. If these are covered in a sticky, tea-colored sludge (which is just oil mixed with moisture), wipe them down with a bit of solvent.
- Test the spring: Springs can lose their tension over years of use. If the spring looks crushed or feels weak, it's probably time to just replace the whole unit.
Why Quality Matters for This Specific Part
It's tempting to grab the cheapest generic valve you find online, but there's a reason why so many manufacturers stick with a control devices inc unloader valve. These things have to handle significant heat. The air coming off a compressor pump is surprisingly hot—often hot enough to melt cheap plastic or degrade low-quality rubber seals in a matter of weeks.
Control Devices Inc. typically uses materials that can handle the "bake-off" that happens during heavy use. If you're running a shop where the compressor is cycling every ten minutes, you need a valve that won't warp or seize. Plus, their designs are usually pretty "trash-tolerant," meaning they can handle a little bit of carbon buildup without failing immediately.
Replacing the Valve: What to Look For
If cleaning doesn't work, you'll need a replacement. When shopping for a new control devices inc unloader valve, don't just go by looks. You need to match a few specific specs.
Check the connection type first. Is it a compression fitting, or does it use NPT (threaded) connections? Most small units use a 1/8" or 1/4" connection. You also need to know if it's a "normally open" or "normally closed" valve, though for standard pressure switches, they usually follow a pretty universal format.
Another thing to check is the PSI rating. Most home and small shop compressors peak at 135 to 175 PSI. You want to make sure the replacement valve is rated for at least that much. Using a valve meant for a small 100 PSI pancake compressor on a big two-stage shop compressor is just asking for a blowout.
Preventive Maintenance for a Longer Life
Once you've got your control devices inc unloader valve working again, you probably want to keep it that way. The biggest enemy of these valves is moisture. When air is compressed, it gets hot, and when it cools down in the tank, it turns into water. If that water sits in the lines, it travels back to the valve and causes rust or gunk.
The best thing you can do is drain your tank regularly. I know, it's a chore and it's loud, but it's the single most important thing for the health of your unloader valve. If you're really serious about it, you can install an automatic tank drain. This keeps the air in the lines drier and prevents that "sludge" from ever forming in the first place.
Also, keep an eye on your air filter. If your pump is sucking in dirty air, some of that dust is going to end up in your valve. A clean filter means clean air, which means a happy unloader valve.
Wrapping It Up
At the end of the day, a control devices inc unloader valve is a simple but vital part of your pneumatic setup. It's the difference between a machine that hums to life effortlessly and one that sits there straining until it breaks. If you're hearing weird hisses or your motor is struggling to kick over, don't assume the worst. Take ten minutes to look at the unloader. More often than not, a quick cleaning or a twenty-dollar replacement part is all you need to get back to work.
It might not be the most glamorous part of your tool kit, but it's definitely one of the hardest working. Take care of it, keep your air dry, and your compressor will probably outlast your current project list by a long shot.