Leaving air preesure in the Compressor tank

[MilDoc]

I only have a small pancake compressor. When in use it's at 90 psi. At the end of the day I bleed it down to 20-25, then drain. I was told by a friend who has had several compressors that draining under full pressure can be dangerous because the drain cock is not rated for that pressure while the bleed cock is.

[LCHIEN]

.... Despite all my efforts to tighten things up, it leaks. It drives my nailers fine when pumped to 90 psi, if you turn it off, tank will go from 90 to 0 overnight. I probably should replace it, but as long as this one works, just can't seem to get around to it. Maybe when there is some killer deal available...

Soapy water can be your friend.

[mpc]

I have a Craftsman unit, 2HP with 20 gallon tank, oil style compressor. It's rated for 6.something CFM at 90psi - a typical "mid-size" compressor. I always open the bottom drain to bleed the air pressure and water at the end of the day. I've never heard of lowering the air pressure first and THEN opening the drain. Mine spits out a couple spoonfuls of clean water spray... in bursts. It'll spray for a minute or two, then slow down even though there is a lot of pressure still in the tank - the blasting air cools down a lot and the water actually freezes in the drain valve. A few seconds later the lack of airflow lets it warm up and melt the ice - BANG! and it drains for a while longer. Over and over... PPPSSSHSSTTssshtt........BANG! PPPHSSSSHSTTshshshst....BANG!
It's loud too. I cringe when I have to lean right next to this thing to open the drain valve.

I use it maybe once a month. It sits at the back end of the garage, against a bedroom wall. If I ever screw up and back up the car too far I'll nail the handle and valve assembly of the compressor. So I don't want it pressurized.

mpc

[jackellis]

It's too early out here to think but as I was reading this last post, it suddenly dawned on me that the temp drop might be why for larger compressors it's a good idea to bleed first and then drain.

[reddog552]

Compressor On /OFF

I have installed quit a few compressor stations.thet allways have a auto water drain programable for time between purge and duration. Also have inline filter-drains at work station.As for shutting off wen not in use Ive seen both.I think with proper maint.ON/ OFF is a moot point

[scorrpio]

Soapy water can be your friend.

I got Big Blue and know how to use it - the problem is not finding WHERE it leaks. The problem is stopping it from doing so. The leaks are in the manifold/regulator assembly of the compressor.

[Stytooner]

I leave everything on and turn my shop off everyday or night. I use the circuit breaker to switch it. It seems to woirk very well. Doesn't overcharge batteries and keeps the comp. at bay.
I drain when I notice moisture in the line. Otherwise, I just rarely think about it.

[Slik Geek]

Anyone understand the reason behind releasing the air pressure before draining suggestions?

I believe that the idea is to relieve the pressure until it reaches 20 to 30 psi, and then open the drain valve.

On my compressor, the bleed valve consists of a screw that compresses a rubber (or a similar soft material) seal. I suspect that bleeding it at high pressures may damage the rubber seal. It is likely fine at full pressure when the valve is closed, since the screw is compressing the seal. When opened, the compressive support is lost, and perhaps the pressure differential is more than the rubber can handle.

[Thom2]

I believe that the idea is to relieve the pressure until it reaches 20 to 30 psi, and then open the drain valve.

On my compressor, the bleed valve consists of a screw that compresses a rubber (or a similar soft material) seal. I suspect that bleeding it at high pressures may damage the rubber seal. It is likely fine at full pressure when the valve is closed, since the screw is compressing the seal. When opened, the compressive support is lost, and perhaps the pressure differential is more than the rubber can handle.

Anyone understand the reason behind releasing the air pressure before draining suggestions?

I think it's a simple safety issue, IIRC (in extreme cases) compressed air can actually penetrate your skin and induce air bubbles into your blood stream, which can then lead to death. AFAIK, even dusting yourself off with a compressed air line is a no-no in the OSHA book.

At 130psi, cracking the bleed valve (especially if it's under the compressor) can put your hand in a spot that is easily in the stream of compressed air.


At least that's my guess

[Jeffrey Schronce]

Own a small PC pancake compressor. It is installed in attic above to reduce noise. I have a regulator at shop level. It is on its own dedicated circuit (uses circuit DC used to be on) and I leave it plugged in and on. I drain the compressor when my nail guns spit water! I do not use it for finishing. I only use nail guns for very rough work. Usually used for bicycles, footballs, etc. I know the tank will rust. And in 10 years I will replace the compressor.

[LCHIEN]

fortunately air compressor failures tend to be less than explosive.
Although there's a lot of energy stored in a compressor, it tends to not be able to release all at once.

The tanks don't explode, they rust out and rusting is a slow business, it'll start a small leak and hiss away causing the motor to run more often.

Unless you are dumb enough to use pastic pipe, the pipes don't explode but generally tend to split and not throw stuff. Air hoses split or develop holes. About the worst is the end of an unrestrained hose will be flapping around and beat up everything in sight.

A compressor with a total leak (broken hose, pipe or big hole in the tank will run continuously and may burn up or sieze up as a result - a possible fire hazard I suppose, if the breakers don't catch it.

All in all, leaving a compressor on 24/7 in your shop is not the worst thing you could do.

[Sid]

Replaced draincock with ball valve

I believe that the idea is to relieve the pressure until it reaches 20 to 30 psi, and then open the drain valve.

On my compressor, the bleed valve consists of a screw that compresses a rubber (or a similar soft material) seal. I suspect that bleeding it at high pressures may damage the rubber seal. It is likely fine at full pressure when the valve is closed, since the screw is compressing the seal. When opened, the compressive support is lost, and perhaps the pressure differential is more than the rubber can handle.

I replaced the cheap draincock on my tank with a brass elbow fitting, a 6" pipe nipple, a ball valve, and a barbed nozzel for some flexible plastic tubing. The water collects in the pipe nipple, perhaps preventing rust in the bottom of the tank, the ball valve is much more accessible and controllable than the original valve, and the tubing can discharge in a nearby floor drain. I open the ball valve very slightly to drain the water under full pressure, and leave the tank under pressure.

Given that I can safely drain the water at full pressure, I'd like more info on leaving the tank at full pressure. I wonder if the flexing caused by wide pressure fuctuations would induce more metal fatigue than just leaving the tank at high pressure.

Sid

[cwsmith]

I've worked in the compressor industry for more than 30 years as a technical writer and illustrator. The first third of that was with Ingersoll-Rand's Air Compressor Division, and the remaining years was with the Process Compressor Division (petro-chemical applications). I have also owned a couple of compressors, with the current unit being a cheapo 33-gal, NL Craftsman (made by DeVilbiss). As you may imagine, my kind of work kept me in touch with technical publications, engineering, field service, technical training, and general product support and marketing functions.

So, what do I do with my own compressor? Well, depending on how long I'm going to be away from using the compressor, depends on how I leave it. If I plan on using it frequently over the next few days, I leave the pressure in the tank. If not, then I bleed off the air, using the moisture draincock at the bottom of the tank. This also facilitates blowing out any condensate that may have accumulated in the tank.

While it certainly would be a cautionary step, to drain the condensate every time I use the compressor, I really don't. I simply don't use it enough in one day to accumulate anything. But I do drain it at the end of any work session, which may be a few days. Also, when I feel I'm not going to be using the compressor for awhile, I drain the tank of both air and condensate. Generally speaking, I simply don't get much condensate build-up with a few hours use, even if it's over a few days. But of course, your particular situation should dictate the need, as frequent operation would result in more condensate, especially on humid days. (As the air temperature drops, so does it's ability to hold moisture.)

With industrial operations (including the small, multi-stage units that are used in service stations and auto repair garages), the receiver tanks are rarely, if ever, discharged except during service. However, it is necessary to blow-out the condensate periodically. In most instances, automatic drain trap is almost a necessity, as this is a much overlooked maintenance routine. When moisture accumulates, corrosion of the receiver tank is highly accelerated, and leakage or rupture can occur. While a destructive rupture is rare, it does happen and it can be very dramatic... you don't want to be there!

My old Ingersoll-Rand twin-tank unit got recalled because of defects in the tank that could be evidenced through long-term internal corrosion. It hadn't happened to mine, but I figured what the heck, I needed an upgrade anyway. I did strip the unit of it's regulator, pressure unit and guages, as well as the shut off and drain valves.

The Craftsman 33-gal, had a simple thumb-screw type drain valve that was a bit-difficult to get at, so I replaced it with the draincock from the I-R unit. Similarly, I also installed it's shutoff valve in the discharge line, before the quick-connect coupler (and after the safety valve). It's a lot easier to connect or disconnect the hose, if their isn't all that tank pressure behind it. Also, those couplers have a tendency to get dirty and leak.

Key to long-term safety and operation is to just get into the habit of keeping the compressor clean, changing the oil and intake filter as dictated by your use, and keep draining any condensate out of the receiver tank. For permanent installations, make sure your lines aren't installed in a manner that would allow condensate to drain back into the compressor. Moisture does NOT compress, and even the slightest amount of moisture that finds itself in the compressor stage, will severly damage the compressor. I've seen 14-inch diameter pistons and cranks that have been totally destroyed by trying to compress a slug of water.

CWS

[gugie]

I put a wind-up timer inline on my compressor

When LOML and I moved into our current house, we knew there was going to be a ton of DIY projects. One of my first purchases after signing the mortgage papers was a 33 gal. compressor. I was using it just about daily for several months, and left it on. In the middle of the night it would start up, so I ran a 1 hr wind-up style timer inline to the power outlet. Now if I want to use the compressor I have to wind up the timer, since after a couple of days leaks in my hose drop pressure down to almost zero. I was thinking of going through and finding and fixing leaks, but it works well as a unintended safety device, IMO.

No more sharp pokes in the ribs at 2 am, either. Well, fewer. I still get them if I'm storing, or it's my turn to go check on a sick kid.