Thread: Picked up a McMillan MA15 Air compressor

Hi All,

I picked up this little gem for a bargain as it had a leak in the pressure switch. Turned out to be a hole in the diaphragm which was easily fixed with some bike tube rubber and a little diy . Much much better and quieter than the cheapo SCA direct-drive unit I have. Now there appears to be a very small hissing leak from the bottom of the filter regulator, there's some sort of coupling on the bottom of it - does anyone know what this is for?

As you can imagine there's not much info about this unit online (it was manufactured in '87), but from what I can tell it has an ABAC twin cylinder pump, Betts 2000watt motor and roughly a 60L receiver. I think the Norgen filter regulator was put on by one of the previous owners judging by the hosing. It has older style couplers (I think they're Ryco type?) so I'll need to get some of the Nitto type on there. What brands do people recommend for fittings and couplers? would rather not cheap out on something that can easily leak.

I'm also looking to spruce it up a bit, things like a quick drain release valve, maybe new gauges in Psi, new filter regulator, etc. any suggestions highly welcome.
and if anyone has any more info on this compressor please feel free. Would be good to know air displacement figures..

Thanks for reading! and we all love pics...

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The "coupling" on the filter reg could be an auto drain valve. They can sometimes hiss a bit if they don't re-seat properly - could be a bit of grit or something. Disassemble and clean...

Michael

> Now there appears to be a very small hissing leak from the bottom of the
> filter regulator, there's some sort of coupling on the bottom of it - does
> anyone know what this is for?

Several possibilities:

- very basic filter bowls just have a schrader valve at the bottom - that is the same valve that you find in a car tyre stem. You press on the valve to release the water and oil slurry inside the bowl.

- better filter bowls have a tap valve that you can unscrew to drain the water. Sometimes there is also a push fitting for a plastic hose to guide the drain water into a container or onto the floor, instead of onto your fingers and the wall behind...

- even better filter bowls have a floater inside. When water collects in the bowl, the floater rises and eventually opens a valve at the bottom to drain the water. Its an automatic drain, so you do not have to check and drain regularly. This type of floater valver often hisses for some 30 seconds to a couple minutes when the compressors starts and pressure is being built up, until the pressure is large enough to positively shut the automatic valve. The process can be helped by tapping onto bowl.



> It has older style couplers (I think they're Ryco type?) so I'll need to get some
> of the Nitto type on there. What brands do people recommend for fittings and
> couplers? would rather not cheap out on something that can easily leak.

I buy only genuine Japan made Nitto couplers, after having made my bad experiences. They are made from Stainless and do not rust away after a year outside like the Chinese "Nitto type" couplers. Nor are they made of cheap anodised Aluminium like some "big green warehouse" couplers, which get dented and scratched easily. SCA recently had genuine Nitto couplers on special, not much more expensive than the warehouse crap.


I use wherever possible push fittings and Polyuretane hose (its the flexible stuff, as opposed to the stiff stuff).


> I'm also looking to spruce it up a bit, things like a quick drain release valve, maybe new gauges in
> Psi, new filter regulator, etc. any suggestions highly welcome. and if anyone has any more info on
> this compressor please feel free. Would be good to know air displacement figures..


I just bought a couple months or so ago from SCA an almost identical compressor, brand name Stanley. It has the same two stage compressor as yours, just instead of being Italian it is a China made copy. But I have the impression it is very well made for a Chinese clone. It comes with 8mm push fittings and plastic hose couplers. It holds pressure for several weeks when not used and unplugged. I think this is good value for $399 (I believe the special is on again right now at SCA, and if you join their club you even get another $10 off).

If you need parts list and compressor data, I can scan my manual...

Originally Posted by cba_melbourne

I just bought a couple months or so ago from SCA an almost identical compressor, brand name Stanley. It has the same two stage compressor as yours, just instead of being Italian it is a China made copy. But I have the impression it is very well made for a Chinese clone. It comes with 8mm push fittings and plastic hose couplers. It holds pressure for several weeks when not used and unplugged. I think this is good value for $399 (I believe the special is on again right now at SCA, and if you join their club you even get another $10 off).

Thanks Chris,
I am looking to either go to a much bigger compressor OR run a second smaller unit in tandem with the 3hp unit i already have. This info might just lead me to buy a stanley tomorrow.....

Nice pick up there Dorikin! Those old compressors just seem to go and go, mine is similar with the 2 stage Ingersol-Rand pump. The one thing i will say is don't skimp on a new reg if you buy one. The cheap ones often deliver full pressure to start with then come down to the set pressure, and often can't keep up with the supply needed.

Ew

Originally Posted by cba_melbourne

Several possibilities:

- very basic filter bowls just have a schrader valve at the bottom - that is the same valve that you find in a car tyre stem. You press on the valve to release the water and oil slurry inside the bowl.

- better filter bowls have a tap valve that you can unscrew to drain the water. Sometimes there is also a push fitting for a plastic hose to guide the drain water into a container or onto the floor, instead of onto your fingers and the wall behind...

- even better filter bowls have a floater inside. When water collects in the bowl, the floater rises and eventually opens a valve at the bottom to drain the water. Its an automatic drain, so you do not have to check and drain regularly. This type of floater valver often hisses for some 30 seconds to a couple minutes when the compressors starts and pressure is being built up, until the pressure is large enough to positively shut the automatic valve. The process can be helped by tapping onto bowl.

I think you're definitely on the money with the second type. The coupler has a valve inside it that can release pressure/water and it looks like it will accept some form of fitting for a drain hose

Had a quick look over SCA website and found this 2.5hp Stanley unit (SuperCheap website). Puts out 190L/min FAD, equates to something like 6.7CFM which is whereabouts what I would put the McMillan compressor at.

Originally Posted by Ueee

Thanks Chris,
Nice pick up there Dorikin! Those old compressors just seem to go and go, mine is similar with the 2 stage Ingersol-Rand pump. The one thing i will say is don't skimp on a new reg if you buy one. The cheap ones often deliver full pressure to start with then come down to the set pressure, and often can't keep up with the supply needed.

Will keep that in mind Thanks!
One thing I have noticed is the receiver is rated up to 1100kPa (roughly 160Psi) which is also when the pressure switch cuts off but the regulator maxes out at 150Psi so it bleeds out around 10Psi when the compressor cuts out. Is 160Psi max pressure too high and should I set it a bit lower?
I know this will depend on usage and the tools requirement but I'm thinking most regulators I've seen are 125-150Psi Max so someone in the past may have incorrectly set the pressure switch cut-in/cut-out range too high??

Mine is set to cut out at 150psi. It has a 160psi relief valve. whilst it won't keep up with the sandblaster (reason for needing a bigger unit) the first 30 secs of pulling the trigger works magically with the higher pressure.

Ew

From what I remember of my days a Sullair, Atlas Copco & Wreckair; a 2hp motor will give a consistent 8cfm...I have an older Vee Twin McMillan which is some 25 plus years old and still going strong.... Just drain the pressure vessel regularly and change the compressor oil annual....also I've used the old brass Ryco couplings for years both in industry & here at home and had no issues......Good purchase sir, well done.....

I have something pretty close to that(though painted a different color ) An SCD Ingersoll-Rand.
It was sold as 14CFM(also in 1987, $780)
It has the same Betts motor, it's two cylinder single stage.
There are a couple of differences, mine has double the number of cooling fins on the cylinders(like the manual)
Yours has the same intake casting as the manual(mine doesnt have the casting, the plastic air filter holder bolts directly to the head)
Mine has a 1090kpa receiver, but the compressor is only rated at 862kPa(125psi)

I'll scan the rest of the manual and add shortly, for what its worth(if anything).

Stuart


p.s. maybe one was copied from the other?

Nice pick up Dorkin.

Originally Posted by dorikin

. . . . .I'm also looking to spruce it up a bit, things like a quick drain release valve, maybe new gauges in Psi, new filter regulator, etc. any suggestions highly welcome.

On my old $199 Bunnings special. I put a small retic solenoid connected to a 24V transformer on the drain valve so it could be drained at the flip of a switch. This worked well so I put a similar valve on my 3P Clisby. This valve is step up to auto drain and turn the motor off at 9pm every night. The motor is left in an off state till I restart it.

Originally Posted by BobL

Nice pick up Dorkin.



On my old $199 Bunnings special. I put a small retic solenoid connected to a 24V transformer on the drain valve so it could be drained at the flip of a switch. This worked well so I put a similar valve on my 3P Clisby. This valve is step up to auto drain and turn the motor off at 9pm every night. The motor is left in an off state till I restart it.

For AU$29.89 including the postage from Hong-Kong one can buy an automatic, electronic timer controlled air compressor water drain valve. It has an adjustable interval time of 0.5 to 45 minutes, and an adjustable drain opening time of 0.5 to 0 seconds. It runs on either 24VDC or 110VAC or 220VAC. The last time I looked at such a device it did cost something like $150. But now, at under $30, I am considering installing one each to both compressors I have:

http://www.ebay.com.au/itm/Integrate...item3ce8241ae2

Originally Posted by cba_melbourne

For AU$29.89 including the postage from Hong-Kong one can buy an automatic, electronic timer controlled air compressor water drain valve. It has an adjustable interval time of 0.5 to 45 minutes, and an adjustable drain opening time of 0.5 to 0 seconds.

Looks good. BTW the opening time is 0.5 to 10 secs. Would have liked to see a little longer interval time available for light compressor use. I guess you can always switch it on and off as required.

Originally Posted by BobL

Looks good. BTW the opening time is 0.5 to 10 secs. Would have liked to see a little longer interval time available for light compressor use. I guess you can always switch it on and off as required.

Bob, I install machines that require a constant flow of about 800L/h compressed clean and dry air, nonstop 24h/7d. Some smaller customers try to get by for the first years with a little oil free piston compressor. Because of the need for a membrane dryer, the compressors will run at a very high duty cycle of 50 to 70%. The best brand name piston compressors last about 18 months, Taiwanese low cost compressors about 4-6 months. That is about as heavy duty use as I can think of, and the compressors produce lots and lots of water. The automatic drain valves are usually set to something like 5 seconds opening time every 15 minutes.

In a home use application, the average duty cycle over the whole year is far less than 1%. In my case, I would think my two compressor run together less than 50 hours a year. I believe a drain valve setting of 0.5s opening time every 45min will be plenty to keep the receiver tank free of liquid water, without by itself causing the compressor to cycle more than just once every week or so because of the extra air use by a drain valve.

Originally Posted by cba_melbourne

In a home use application, the average duty cycle over the whole year is far less than 1%. In my case, I would think my two compressor run together less than 50 hours a year.

That's pretty close to what I estimate I would use.

I believe a drain valve setting of 0.5s opening time every 45min will be plenty to keep the receiver tank free of liquid water, without by itself causing the compressor to cycle more than just once every week or so because of the extra air use by a drain valve.

My compressor has a 70L tank and it loses ~1.5 PSI/s of discharge (a bit more at higher pressure and a bit less at lower pressures).
0.5s every 45 minutes means 16s of discharge a day or 112s of discharge a week which is equivalent to ~ 168 PSI,
The compressor is set up with a 45 PSI range so the 168 PSI is equivalent to about 4 additional recharges a week.
Still OK and I guess a simple tap on the drain could restrict the discharge to whatever one desired.

I like the idea of little and often as it will remove the water asap rather than sitting around in the tank for too long.

I was sandblasting a bit earlier and noticed moisture coming out of the gun. My water trap looked ok, so I thought I would drain the tank. 2l of water later AMD I know why I was having issues......

Ew

Originally Posted by Ueee

I was sandblasting a bit earlier and noticed moisture coming out of the gun. My water trap looked ok, so I thought I would drain the tank. 2l of water later AMD I know why I was having issues......

Ew

Hi Ew.
what size is your unit that you use for sandblasting ? i'm in a market for one that suit a small sandblast , any idea ?
cheers
Peter