Compressor modification

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Ride_on
Posts: 2265
Joined: 26 May 2009 05:34 pm
Location: Belfast, N. Ireland

Compressor modification

Post by Ride_on » 09 Sep 2010 02:32 pm

I've worn out my drill using it as a brush and drum sander etc, and I also need to be able to spray underseal. I only have a old Clarke Jumbo compressor without a reservoir, but looking on Ebay I can get what I think are the necessary parts to convert it.

Mainly I need a receiver;
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT

and a pressure switch
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT

Also a regulator, but this is more straight forward with recognised connectors etc

My main concern is connecting up the pressure switch, there is some mention of a blow off function which I think I need so the compressor is not loaded when it starts. There seems to be an elbow/check valve on the tank and I am guessing this should connect to the compressor and the blow off connection (the 6.5mm connector behind the main 3 output manifold) in the pressure switch. I don't understand why this is 6.5mm in the picture, although the text says its 1/4" also.

Anyone have a compressor/receiver can confirm the connections?
1980 345 DL_______1987 360 GLE (project car restored to GLT spec and B230FT'd)
1984 360 GLT______1987 360 GLT
1983 360 GLS______1989 360 GLE
1985 340 GL_______1986 340 1.4
1985 360 GLS______1995 940 SE 2.3 Turbo Estate (daily)
1987 340 GL 1.7

Ride_on
Posts: 2265
Joined: 26 May 2009 05:34 pm
Location: Belfast, N. Ireland

Re: Compressor modification

Post by Ride_on » 21 Oct 2010 01:51 pm

Well after several weeks of research, buying and trying stuff I now have a fairly capable air system, but the sellers don't make it easy. Wading through the seller lies on part specifications has been particularly difficult, as well as many poor quality or poor performance items. Hopefully this story will help anyone considering an air system.

The story;

Main requirements;
Underseal with around 10cfm at 90psi
Sandblast with around 15cfm at 100psi

Started with compressor only, capable of 3.4cfm and 116psi (not necessarily at the same time)

I considered buying a complete system for about £130, and this would give you a 2HP motor and 8 or 9 cfm, but it was a lie. It is only rated for 20% duty cycle so the actual average air delivery is lower than my 3.4cfm unit which is rated for continuous use. This is why alot of cheap compressors expire fairly quickly. The max cfm depends on the connectors in the air tank, how long you can use it for depends on the tank size. It is rare for even a medium sized professional application to not require tank recharging gaps, ie the compressor normally provides less air than the most heavy application uses. So its not so dependant on the motor size, which many are now heavily advertising.

I upgraded the compressor with the ebay air receiver, which had water drain and input valve and output mount for the switch, a pressure switch/relief valve and a tank pressure gauge. Getting the necessary connectors was tricky as it was a mix of plumbing stuff (compression joints, BSP joints) and hydraulic standards (flared). I used a long copper pipe from the compressor to the receiver to help dissipate heat. The tank supplier eventually sent the flared connector for free, as they had claimed 'new' but it clearly was a recovered tank, dented covered in oil etc.

The air receiver was then upgraded further with a gas bottle of about 2x the size using a bulkhead connector from RS because it has the M20x1.5 thread needed for the gas pigtail (no other plumbing stuff uses metric AFAIK) to convert to 1/4" BSP. I have another gas bottle and connector ready as the current system can only supply for about 1min sand blasting before recharging. I had ordered a 20mm thread to 10mm plastic push-in fitting from Hong Kong but it didn't work as the threads where a different pitch.

The pressure switch has 3 outputs and is supplied with blanking studs, however these where BSPP (Parallel threads) and should have been BSPT (tapered) and where very difficult to seal. In the end I used all the outputs.
IMG_2550.JPG
Compressor with propane tank
I used 10mm plastic rigid pipe for the garage air system, the compressor is in another room away from the dust and paint. I got an unwanted RS 30m reel for about £12 from ebay auction, which was good value. It enabled me to double up the piping as with hindsight the 10mm only had 7.5mm internal dia. The Pressure switch manifold also has quite small opening/restriction (half the diameter of the female thread), although these could be drilled out, paralleling up with 2 also helps the frictional losses in the pipe. Push-in connector seal pretty well and are easy to use/cut, unlike the BSP system, although it needs to be unstressed and can come out if you push sideways on it.

The BSP system is a bit outdated but still used. It normally requires a tapered male thread going into a parallel female thread. It seems to be confused with hydraulic conical joints (parallel thread) that can swivel and the length and other types that need a washer with a controlled thread length. As a result alot of items are supplied with parallel male threads, or state tapered and are actually parallel. Many sellers (particularly ebay) don't know what they are selling. I think parallel threads are best sealed with a washer if it has a base to sit on, but I have found a semi solid paste (Pritt stick type dispenser) works fairly well depending on how loose the threads are, otherwise loads of PTFE tape works.

I intended to install the regulator/water trap/filter on the wall in the garage and ordered what I thought was an adequately spec'd item and good quality branded at £17, rrp £35. It was a Sealey with 76cfm max rating and 2 output valves. As I have now found out 'max cfm' is FAD (Free Air Delivery) and so represents the the air flow at which the item is completely useless. Air flow should always be rated with pressure drop, and FAD means pressure drop to atmospheric pressure, or around 86psi drop with a rated pressure of 100psi (atmospheric is about 14psi). So pressure drop was my problem, using the sandblaster and set the regulator to 100psi the pressure was dropping by >25psi on the regulator when pulling the trigger. Silly me for thinking the regulator would regulate! For sand blasting I was able to increase the pressure (gun has 175psi max written on it, but packaging says 110) and take the regulator out of the loop basically, this allowed me to get 90-100psi depending on the state of the tank (the switch comes on at 90psi and off at 120), so I knew it wasn't the supply that was the problem.

As it happened the regulator was faulty and one of the output valves leaked badly so I asked for a return/replacement and they sent one out and let me keep the old one for parts. I thought this would allow me to double the air flow capability and half the pressure drop if I put these in parallel, as I already had most of the parts.. No such luck, it barely improved, and I was still getting about 20psi drop, that is alot to lose in sandblasting or any air tool, and you use alot more material due to the lack of force.

I started looking for a replacement and discovered that the bigger the port the bigger the regulator and associated FAD spec, even though a much smaller port is not restrictive in itself, some of the connectors have smaller internal dia. I ended up getting one spec'd at 7000l/m (250cfm) with a 1" port, it is huge but only cost about £45, its an SMC copy but seems to work ok. The pressure gauge was smashed and bent on delivery, it was separate and not much protected in the box so the 1kg regulator killed it, the supplier sent out a replacement quickly. It works well for pressure drop, now <4psi, although drifts up when left standing, I also added a T and ball valves to isolate the tools. I have a long (cheap) 8mm ID hose, for low flow tools, and a more expensive 10mm ID/5m hose with no quick couplings for the high flow stuff. The problem with the hoses is that 8mm is ok for flow but the hose tails need to be about 5mm ID, which is restrictive, and even smaller if you use a rotating/swivel coupling. Forget about using cheap universal joint at the tool these are even more restrictive.
IMG_2549.JPG
Old and new Regulators
I was also confused and taken in by quick release connectors, I initially wanted to use the common industry standard, which are PCL airflow/vertex types common in the UK and cheap copies available on ebay. As it happens these are rubbish, and only rated at 43cfm FAD with just a 4mm dia opening. Euro ones are significantly better with 7.4mm dia opening (FAD >120cfm I think), but more expensive, cheapest I could find is Draper and most ebay ones seem to be this. Alot of tools are supplied with a euro coupling (the cheap end).
IMG_2551.JPG
Quick coupling comparison
Other air tools I got are a die grinder (useful for getting into tight areas) (tools zone £15) and a 3/8" wrench (SIP kit £23, rrp £40), good again for tight access, you don't have to swing it. Watch out for cheap ebay stuff that is US import and has NPT threads on it instead of BSP.
1980 345 DL_______1987 360 GLE (project car restored to GLT spec and B230FT'd)
1984 360 GLT______1987 360 GLT
1983 360 GLS______1989 360 GLE
1985 340 GL_______1986 340 1.4
1985 360 GLS______1995 940 SE 2.3 Turbo Estate (daily)
1987 340 GL 1.7

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