Thread: Cold weather air compressor

I have a similar issue with my compressor.
I've owned it for many years (around 10 years) and while we lived in QLD it worked fine, but since moving to Armidale it doesn't like startups - especially when it's cold. Also doesn't use any oil.

Maybe it's just getting old ???

I once knew a bloke who owned an old grey diesel Fergie who used to light a fire under it's sump before he tried to start it ....

You have probably tried this but just in case you haven't. open the air outlet on the compressor before switching it on. This creates less load on the motor and should run more freely. When the motor warms up, switch the air outlet valve off so the compressor can build up pressure.
It's worth a shot. Good luck.

Yeah, I've gotten into the habit of letting the tank pressure drop very low and then starting the compressor - normally works well, although can still struggle a little bit on very cold mornings.
I've also disconnected the pump outlet pipe and the compressor ran very well (just didn't put any air into the tank).

There is an unloading valve on many compressors that unloads the compressor cylinder (not the air tank) on shut down. This way the motor doesn't have to start against a load. Also, is there a lighter oil available for cold weather operations at your air tool dealer?

I have a lot of experience with motors and engines in very cold (Arctic) temperatures. The reliable fix is moving to a warmer climate

Thanks for the replies guys. What exactly do you mean by the air outlet? Do you mean where you connect the hose? Because this closes automatically unless a hose is inserted.

Sorry, i'm a newbie to compressors.

Sounds like the unloader isn't working properly
Does the compressor noise change after it has been running for a few moments, usually the compressor runs and you should hear the sound of air being vented to the atmosphere then a valve closes then the unit loads up and the motor noise changes if this isn't happening then the unloader isn't working properly.

Oil viscosity matters, but there is also the shrinkage of all metal parts (like pistons and cylinder wall inner diameters) in severe cold, resulting in tighter fits and more friction. This phenomenon is also known in sleeve bearings, i've come across electric motors with such bearings that will run well in summer and won't budge in winter, and not just because the lube oil in the bearings becomes more syrupy in the cold. The experience of VernonV may also underline this, since his compressor was oilless and was sluggish in the cold nonetheless.

A tighter cold fit can't be remedied, but making the compressor's life easier during startup is certainly worthwhile. Warming up under no-load was mentioned several times. In older types of oil lubricated pneumatic hammer drills, running them no-load for a few minutes before starting real work, was even specifically mentioned in their manuals. Only when motor reserves were cranked up and lubricating technology became much better in the last 10 years, Hitachi and their colleagues dared to claim "excellent cold startup properties" in their brochures.

Warming up from the outside with a heat source was also mentioned. If the compressor can be moved on wheels, a heated room would be nice but the lady of the house will probably kick it out. If the compressor is a stationary type in a cold shed, warming the pump unit with waxine tea lights or candles can help. If the shed is not to drafty, these lights will not be blown out and will give some heat for several hours. Placing a few of these underneath or closely around the pump unit will warm it some 5 to 10 degrees Centigrade above the room temperature. External heat sources are also used for large diesel engines. Diesel locomotives meant for immediate service on cold mornings are known to have electric circulation pumps for their cooling water, which is heated at night by means of a diesel oil fired burner. These locomotives are literally "plugged in" in the mains at night, either in the shed or outside in the yard.

Always advisable is a proper choice of crankcase oil. There is a vast choice of reciprocating compressor oils and even a few types behaving very well in cold climates. The figure to watch for is the "viscosity index", which must be low (preferably below 100). Such oil will already be thin fluid in the cold and hence will not have many lubricating reserves at extreme heat, but that will hardly be an issue. The SAE-grade will be around 5W20 or 10W20, which would characterise as a "car's winter oil". Not any winter oil will do however, a good low visc compressor oil (which for cold use is best chosen in a synthetic variant) will have totally different additives and chemical charachteristics than combustion engine winter oil does.

Compressor oils are a science on their own, their is plenty of stuff to read in the internet, like these examples:

http://www.manufacturingtalk.com/news/klu/klu104.html

http://www.sinwal.com/data/Nov%202005%20Compressor.pdf

http://www.ecompressedair.com/lubric...ter.shtml#spec

There are many brands, all offering many types of compressor oil. Good choices for cold use seem to be Amsoil Scirocco, Kaeser 460 and SX46.
Do get in contact with your compressor manufacturer as well, for their specific advice on this. If your compressor runs in very cold conditions all the time and the brand is a serious professional one, they may even have adapted cylinder or piston sizes for such occasions. I know that eg. Boge and Atlas Copco used to offer various specifications according to climatic conditions. If startup problems occur all the time, you may also need to fit a larger motor, since the heavier operating circumstances may be rather "nominal" than sporadic.

regards

gerhard

Back with two additions. I re-read the other posts, and Vernon's compressor probably had oil in it, but he wrote that none of it was used in cold weather. So i misunderstood that, but it doesn't matter, the issue of shrinkage in the cold and resulting friction is still valid.

I also read about the suggestion of blowing off the tank and let the compressor fill it from zero. I guess you are reluctant to do that, since it's a waste of good energy, but it's a very good idea. You wrote you couldn't find a no-load valve on your compressor and that may probably be because none is fitted. Not many nowadays average compressors are featured with one, only the large industrial stationary types with three phase motors have one as standard, where it is usually combined with the delta/triangle startup time-delayed relay. The three phase motor starts up with its stator coils connected in "triangle mode", which reduces startup current and wear on the drive belt. During this startup time on reduced Amps, the motor cannot deliver full power, so the solenoid operated no-load valve vents the pressure circuit between the exhaust valve and the tank. When the motor reaches full idle rpm (the time of which is set in the relay), the coils are switched in "delta mode" and the motor can deliver full power. At that same moment, the no-load release valve is closed and pressure can build up.

Releasing the entire tank contents after jobs ensures that the compressor can run fairly freely for considerable time on every new startup. When the motor starts to meet resistance from the built up pressure in the tank, several minutes will already have passed, which is enough to have heated up the cylinder wall sufficiently for decent running and proper lubrication. Also, draining the tank on regular intervals ensures proper drainage of condensed water, which will build up quicker with cold weather and will rust the tank walls from the inside, especially with oxygen-rich mountain air. I save my cleaning jobs for moments of tank drainage. I use two-thirds to blow clean my tools and release the rest through the tank's bottom tap to get rid of the condensate, so the energy need not all be wasted.

greetings

gerhard

What about wrapping some water pipe heating tape or some tank heating tape around the compressor. If you turn that on for 30 minutes before you start it should heat it up and expand things so it can start easily.

BTW I notice the same problem here in WA on a cold morning ie 5ºC?

Cheers

Originally Posted by gerhard

Oil viscosity matters, but there is also the shrinkage of all metal parts (like pistons and cylinder wall inner diameters) in severe cold, resulting in tighter fits and more friction.

Have never heard of or seen seizure of a piston in a cylinder due to the cold If the cylinder shrinks then so does the piston. I have seen piston rings and piston seize due to piston cooling failure and the piston expanded but if the engine is allowed to heat up and cool at the same rate there is no problem

Originally Posted by gerhard

External heat sources are also used for large diesel engines. Diesel locomotives meant for immediate service on cold mornings are known to have electric circulation pumps for their cooling water, which is heated at night by means of a diesel oil fired burner. These locomotives are literally "plugged in" in the mains at night, either in the shed or outside in the yard.

All large diesels require heating to limit damage and excessive wear at start up regardless of the air temp , the heating is usually done with steam or electric coils and 50 to 55 deg's centergrade is the norm but we are talking about a small comercial Air Compressor

Originally Posted by gerhard

You wrote you couldn't find a no-load valve on your compressor and that may probably be because none is fitted. Not many nowadays average compressors are featured with one, only the large industrial stationary types with three phase motors have one as standard,

All Recricating compressors Have an unloader if there is not an unloader fitted to an air compressor you will not be able to start it , no recrip compressors start under full load

Originally Posted by gerhard

it is usually combined with the delta/triangle startup time-delayed relay. The three phase motor starts up with its stator coils connected in "triangle mode", which reduces startup current and wear on the drive belt. During this startup time on reduced Amps, the motor cannot deliver full power, so the solenoid operated no-load valve vents the pressure circuit between the exhaust valve and the tank. When the motor reaches full idle rpm (the time of which is set in the relay), the coils are switched in "delta mode" and the motor can deliver full power.

Delta /triangle do you mean star /delta where the " triangle " is infact the delta
henlan77 would be talking about a small direct drive compressor and if the unloader is working correctly could then look at a lighter oil , but check with the supplier or manufacturer cause if you lower the viscosity too much you can do damage to the unit when it gets up to running temp.

Wow, that's a lot of information, thanks for your time guys.
However I am only talking about a $200 40 litre direct drive portable compressor here.

Is there a way to check if the unloader is working properly?

As I said in an earlier post
"Does the compressor noise change after it has been running for a few moments, usually the compressor runs and you should hear the sound of air being vented to the atmosphere then a valve closes then the unit loads up and the motor noise changes if this isn't happening then the unloader isn't working properly. "
You should hear a hissing noise then a distinct change in noise as the unloader closes and the motor noise will then change pitch this should happen n 30 to 40 seconds or so after the compressor is switched on and starts running

I have the same trouble with a direct drive compressor even with zero pressure.

How about using an old electric blanket over the compressor to get it warmed up a bit before it is started....

I was in the pet store on Sunday and saw one for dogs...low voltage so a lot safer!

Chipman