What air compressor should I buy?

[Mike Nash 2Participant @mikenash2]

For low a low 67 DBA Air compressor that is 100% duty rated so will run all day long then theses look the ticket.

https://www.sprayman.co.uk/product/gentilin-csk240-silent

mike

[Ex contributorParticipant @mgnbuk]

Grit blasting uses a lot of air to do anything meaningful.

I have a small steel blast cabinet & my 2hp direct drive compressor on a 50 litre receiver is not capable of supplying enough air to use it for more than a minute or so before the pressure drops right off. Then a wait until the receiver fills again & another minute of use. The cabinet lives at work now so I can use the works 7.5hp screw compressor to drive it + hooking it up to a dust extractor aids visibility. Even with water traps, the grit (glass beads in my case) gets damp & clogs. A hot air gun dries it it again reasonably quickly.

Before I bought the table top purpose built cabinet, I had built one out of plywood that worked OK using an inexpensive blast gun. Erosion was not a problem during the clean-up of quite corroded BMW motorcycle engine & gearbox castings. This was built & operated while I was at my last employer – more air than at home but no dust extraction there, so even with the cabinet it was a dirty job. With hindisght I would have been better subbing the job out, as it took ages.

I would avoid the cheap "oil free" compressors, as these have a very low duty cycle & die quickly if pushed beyond their meage limits. OK for blowing the odd tyre up, but not much more.

Nigel B.

[Clive FosterParticipant @clivefoster55965]

That Gentilin compressor linked to by Mike Nash looks impressive. Good price too if it is 100% duty cycle at 8 cfm FAD. The sample motor label in the instructions shows 66 %, 20 minutes on – 10 minutes off which sounds more like it.

Have my doubts about naked noise levels as its fundamentally an ordinary oil free piston, with ptfe rings, compressor. A common design for inexpensive Italian compressors. Very similar in concept to my SIP, albeit slower running. Which is way more noisy.

I see they list a cabinet that is said to reduce noise by 12 dBA. I also see they have proper paper air filters on the inlet. Putting proper filters on my Atlas Copco Vee twin made a decent difference to noise. Memo to me :-  try that on my SIP.

Parts and accessory list is interesting **LINK** . Looks a nice concept.

mgnbuk is dead right about life of the simple oil free compressors. The ptfe rings do wear quite quickly. I think the 2,500 hrs before overhaul quoted by Gentilin is optimistic. 1,000 would be good going.

With a big tank its up to sand blasting if the right air size nozzle is used. With a bench top or small cabinet you have to keep waiting for the dust to settle so pressure has time to recover.

Most kits come with too large a nozzle fro a smaller compressor. I was surprsied how small the smallest one Guyson list is. Specified for 10 cfm.

Clive

Edited By Clive Foster on 10/11/2020 10:21:10

Edited By Clive Foster on 10/11/2020 10:21:49

[Dave HalfordParticipant @davehalford22513]

Posted by Iain Downs on 09/11/2020 21:57:19:

I'm having a bit of a rethink. Yes I can get a compressor which is quiet and not too feeble (probably). But for the same or less I can get a much more powerful compressor which is noisy.

My concern is a) the neighbouts and b) my ears, but, I am unlikely to use it often or for continuous work. So with the odd blast of air to clean the mill the motor would rarely start.

If I want to run it continuously I could choose my time of day – and as is (half seriously suggested) above, I can always stick it in a box.

I'm a bit conflicted too as it occured to me that I could spend my (circa £200) Christmas present budget on a quiet compressor or an 8 inch rotary table. I currently have a 4 inch one which swamped my micro mill, but is not working at all well for my new bigger mill (Mainly the problem is clamping work. It turns alright but the bed's so small).

Finally, if I do get a compressor with the aim of occasional sandblasting would a wooden cabinet work or would it get eroded too quickly?

Iain

Stalk Ebay till one like this comes up your way.

Hope you have a big mill, 8" is massive if you ever need to get it on centre and very heavy indeed.

Stone chip sprayed on the wood will stop any erosion if you get the white version it helps with seeing in there.

[Clive FosterParticipant @clivefoster55965]

Concerning sand blasting and compressor size.

Guysons do a useful download giving various useful parameters for sizing sandblasting equipment including the size of air jets for a given blast pressure and CFM. **LINK** .

Home users will probably find a 2 mm noizzle plenty large enough.

Guyson advise that the compressor be at least 50% larger than indicated by nominal air nozzle size for continuous use. Also copes with wear.

Clive

Edited By Clive Foster on 10/11/2020 14:15:12

[Mike Nash 2Participant @mikenash2]

My post was a bit cheeky. I am a member of the forum and have been for a few years. I was looking at small milling machine posts (interested in a VM18 type miller), when I spotted the air compressor posting. Cheeky because the company I work for are the importers of Gentilin. And yes they really are S1 motors therefore 100% duty rated and the CSK240 Ultraquiet models really are 67 dba. We sell them for commercial painting contractors and they run in continuous stop start mode, as we match the spray gun usage exactly to the compressor output. They are not your typical oil free either. Service interval on the CSK240 model is 2500 hours.

[Mike Nash 2Participant @mikenash2]

Posted by Mike Nash 2 on 10/11/2020 16:21:10:

My post was a bit cheeky. I am a member of the forum and have been for a few years. I was looking at small milling machine posts (interested in a VM18 type miller), when I spotted the air compressor posting. Cheeky because the company I work for are the importers of Gentilin. And yes they really are S1 motors therefore 100% duty rated and the CSK240 Ultraquiet models really are 67 dba. We sell them for commercial painting contractors and they run in continuous stop start mode, as we match the spray gun usage exactly to the compressor output. They are not your typical oil free either. Service interval on the CSK240 model is 2500 hours.

Finally I have a Hydrovane PR303e compressor in my garage that I rebuilt as an apprentice at Binks Bullows 40 years ago. It was 20 years old then. It still runs faultlessly. They knew how to engineer stuff back then.

[Clive FosterParticipant @clivefoster55965]

Mike

67 dBA is seriously impressive for a naked aluminium piston compressor. Especially at that speed and output.

I always found the cast iron units were subjectively much quieter. Probably more due to the deeper sound with no annoying high pitched fin ring than actual sound pressure levels.

Sounds like you are supplying them as a (larger) device for similar duties the little Binks-Bullows hydrovane pictured in one of my earlier posts was made for. Nice to know that they really are industrial quality devices.

Looks like the small Hydrovanes have some serious competition. Especially at the offer price. Although hydrovanes come with a bigger tank, absolutely not an advantage for a mobile contractor having to move things around, and vastly greater time between overhauls. If you change the oil at the right intervals.

Lord knows what the equivalent new price of your PR303e would be today. "When I win the lottery" I guess. Lots of re-engineering went into the later models to get the price down to merely expensive!

Clive

[Mike Nash 2Participant @mikenash2]

Posted by Clive Foster on 10/11/2020 16:53:46:

Mike

67 dBA is seriously impressive for a naked aluminium piston compressor. Especially at that speed and output.

I always found the cast iron units were subjectively much quieter. Probably more due to the deeper sound with no annoying high pitched fin ring than actual sound pressure levels.

Sounds like you are supplying them as a (larger) device for similar duties the little Binks-Bullows hydrovane pictured in one of my earlier posts was made for. Nice to know that they really are industrial quality devices.

Looks like the small Hydrovanes have some serious competition. Especially at the offer price. Although hydrovanes come with a bigger tank, absolutely not an advantage for a mobile contractor having to move things around, and vastly greater time between overhauls. If you change the oil at the right intervals.

Lord knows what the equivalent new price of your PR303e would be today. "When I win the lottery" I guess. Lots of re-engineering went into the later models to get the price down to merely expensive!

Clive

Clive they also supply same model ( but sanitised ) for dental surgeries. We supply them for running a spar gun directly, on pressure vessels for workshops in single phase and 3 phase for bigger KW models. As I said they are commercial/ industrial grade so are very reliable. Being oil free then for spray painting they are ideal. I love the patented design of the air end. Brilliant as unlike a Standard piston compressor the, pistons do not pivot on a bearing and crank. The pistons remain parallel in the bores. This ensures maximum contact path of the seals at all times. Hence the reason why they have such a long service interval.
regarding the little PR303 Hydrovane compressor, it would cost about £3000 to buy nowadays! Mind you only a small CFM out put at 30 psi.

[Philip AParticipant @philipa30666]

Hi, just my input from having owned several compressors.

A "proper" compressors output is approx 70% of the quoted figure. So my 14 CFM compressor just about keeps up with a 10 CFM tool.

I had a couple of low cost compressors which quoted 9.6 CFM but couldn't even keep up with a 4 CFM tool. I actually ended up in court making a small claim to get my money back and easily proved my case and won.

I now have a 3HP Italian made compressor and a 4HP Clarke industrial. The latter is cast iron and although it's only slightly quieter, the noise from a cast iron compressor is much lower frequency and more tolerable, it's like listening to a Harley vs a loud scooter.

Some of my neighbours complained about noise so I put the compressors in a sound proof box. That didn't work as I couldn't get enough airflow to keep them cool, even with expensive extractors. I dismantled the box and just placed some plywood with soundproof foam around the compressors and found that made enough difference to keep the neighbours happy. I still have an industrial extactor fan blowing air over the pumps though as the plywood reduces circulation. All works well now.

[Clive FosterParticipant @clivefoster55965]

Phillip

I found that a decent size airbox on the intake side fed via a proper "car size" air filter made a big difference to compressor noise. Removes all the pulsating suction sounds. Breed is unimportant, whatever decent size unit the local breaker has cheap today will do although I used same one as thec ar I was running then and recyled the used air filters discarded at service time.

Can get surprising amounts of surface transmitted noise too. If its on solid tyre wheels switching to pneumatic types all round makes a significant difference. My builds were on solid feet so I laid a tyre or two down flat on it's side and fixed sheet of plywood to it to make a (relatively) isolated support.

For air transmission a pair of slatted / louvred doors mounted face to face with an offset so there is no direct path is quire effective yet allows adequate ventilation so long as there is airspace between. I wonder if setting the pair at 90° would work better. May need a shallow spacer to give enough space for cooling air flow. I imagine anything over around 1/8" between the louvres at their closest point should do.

Clive

[Philip AParticipant @philipa30666]

Posted by Clive Foster on 14/11/2020 11:42:10:

Phillip

I found that a decent size airbox on the intake side fed via a proper "car size" air filter made a big difference to compressor noise. Removes all the pulsating suction sounds. Breed is unimportant, whatever decent size unit the local breaker has cheap today will do although I used same one as thec ar I was running then and recyled the used air filters discarded at service time.

Can get surprising amounts of surface transmitted noise too. If its on solid tyre wheels switching to pneumatic types all round makes a significant difference. My builds were on solid feet so I laid a tyre or two down flat on it's side and fixed sheet of plywood to it to make a (relatively) isolated support.

For air transmission a pair of slatted / louvred doors mounted face to face with an offset so there is no direct path is quire effective yet allows adequate ventilation so long as there is airspace between. I wonder if setting the pair at 90° would work better. May need a shallow spacer to give enough space for cooling air flow. I imagine anything over around 1/8" between the louvres at their closest point should do.

Clive

Yes I keep hearing that fitting an airbox makes a big difference, I might try that.

[Iain DownsParticipant @iaindowns78295]

I thought I'd posted an update before this, but it would appear not.

In the end I have bought both. An 8 inch rotary table from a forum member (and very nice it is, too) and the KIEI compressor mentioned in an early post.

The compressor ended up being on sale for 30% off on 'Black Friday' coming in at around £180 which I thought was a decent price – especially if it delivers to the specs.

But right now, I don't know. Why not? because utterly NOT to my surprise, the compressor comes with an outlet connector which doesn't match the input connectors on the kit I bought at the same time!

Here's what I've got.

The compressor connector thread appears to be 1/2" BSP. Which is to say that a die with that stamped on it screws most of the way in (and similarly on the female thread -and the diameter of the thread is about half an inch). However, the thread appears to be tapered in some way in that i can only screw it about 2/3rds of the way in (and it appears slightly conical to the naked eye).

I don't know if I should try and buy replacement connectors for the compressor (to fit the tools) or if I should try and buy adapters (the compressor is dual outlet).

I have spent a bit of time asking the internet and haven't really ended up with a clear answer. I've also spent a bit of time in Screwfix with a young man who wanted to help but had no idea at all!

I'm clearly expecting much better things from the forum than the internet!

Iain

[Iain DownsParticipant @iaindowns78295]

Oh – and the compressor comes with almost incomprehensible (and badly spelt – even by chinglese standards) instructions, which don't even bother to tell you how to put it together. I've probably done it wrong.

I will let you know if it compresses!

Iain

[Iain DownsParticipant @iaindowns78295]

Further investigation reveals that the BSP with a diameter of around half an inch is a quarter inch BSP. Clearly I had a reality jolt when I read the die.

I also find that BSP Tapered is a thing, so my guess is that this is what I have on the compressor

Iain

[Nick WheelerParticipant @nickwheeler]

Bin the fittings it came with and replace them with standard PCL ones that are available anywhere

[SteviegtrParticipant @steviegtr]

Iain, BSP threads come in 2 types. Parallel or tapered.

As above the PCL fittings are a pretty much industry standard & reasonably reliable.

Steve.

P.S. As NDIY says male only. 

Steve.

Edited By Steviegtr on 27/12/2020 13:41:51

[not done it yetParticipant @notdoneityet]

All female BSP are parallel. The male threads could be either. Low pressure is often taper (fitted with a filler and jointing compound or with PTFE tape. High pressure installations usually include a rubber inserted washer as the seal (Dowty washer).

[Clive FosterParticipant @clivefoster55965]

Either PCL or Euro type will do just fine and are easily obtained. Yours look as if they should be Euro.

If you are a LiDL shopper an advantage of the Euro type is that they periodically do air tools, accessory kits, airlines and sets of connectors of very acceptable quality at economical prices usuing Euro connectors. Good way to get extra equipment. Especially as the prices make "I will only use it a few times." purchases viable.

LiDL prices mean I'm slowly switching from PCL to Euro. Too much invested in PCL to be worth the switch at proper trade supplier prices but its viable at LiDL ones.

The Euro style ones have a larger through bore than PCL so theoretically pass more air at a lower pressure drop. Which may be important for blasting and similar. Must get round to changing the connectors on my blaster to see.

Chinese air connector threads can be obscure, crazy or both. I found one that measured as being Admiralty (obscure) but I suspect it was supposed to be American and the copier cocked up (crazy).

Clive

[Phil PParticipant @philp]

Clive

Just had a read back through this thread and on page 1 you say that you are using your Guyson cabinet to blast at well over 100 psi. I would say that is way too high and you should normally be able to use half that pressure.

You may well accelerate the time taken to do the job, but the blast media breakdown rate will be terrible and you will use a lot more of it. You will also be causing a lot of internal wear to the gun and anything in contact with the moving blast media.

How do I know this ?…..Well I have been chief design engineer at Guyson's for nearly 33 years and I have picked up a few things along the way. My forte is designing the big automated and robotic stuff for production line work, but the basic principles are exactly the same as on the small hand cabinets.

One easy way of getting more from less so to speak, is to get a bigger or additional reservoir on the compressor.
It will not solve the problem entirely but will allow longer spells of blasting before waiting for the compressor to catch up.

I will soon need to get my own blasting facilities sorted out, when I retire I will lose my free access to all the equipment at work.

Phil

[Paul KempParticipant @paulkemp46892]

Posted by not done it yet on 27/12/2020 13:31:35:

All female BSP are parallel. The male threads could be either. Low pressure is often taper (fitted with a filler and jointing compound or with PTFE tape. High pressure installations usually include a rubber inserted washer as the seal (Dowty washer).

Sorry incorrect, all female BSP threads are not parallel, they may also be tapered. You may use a tapered male thread in either a parallel female or tapered female thread these are accepted as sealing on the thread with an accepted compound. Parallel male threads are not considered as sealing on the thread and should not be used with tapered female threads and as correctly stated are sealed with a conforming washer.

Paul.

[Dave HalfordParticipant @davehalford22513]

Ian,

Most air fittings are straight, use PTFE tape. The coiled hose will drive you mad and restrict your flow as well.

Don't forget to fit a filter regulator to replace the joke one and a decent on/off tap.

You can get BSP black iron fittings at your local plumbers merchant

[Clive FosterParticipant @clivefoster55965]

Phil

Thanks for the heads up on pressure for blasting.

Hafta say I just took the advice of a mate who had done a fair bit of blasting professionally, mostly outside stuff and inside huge tanks, but he also had his own cabinet, not Guyson but professional grade, a little bigger than the one I have now and set things to what he said. According to the gauge on the cabinet I have about 80 psi at the gun so its not as bad as it sounds.

I shall have to have play at lower pressures next time. Blasting is not something I do much of. But when my experienced friend moved 150 miles away ….

Clive

[old martParticipant @oldmart]

Loctite make an excellent pipe joint product, 577, where PTFE tape is difficult to apply.

[noel shelleyParticipant @noelshelley55608]

As Has been mentioned earlier, price and quality must be considered. BUT what ever you buy, wire the compressor through a direct on line starter rated for the full load current of your motor !!! Failure to do this will nullify any guarentee. This is NOT to be confused with a No volt release. The quality of many cheaper motors is questionanble and the Non return and unloader valves also ! At least a DOL may save the motor and show up a fault with out smoke. If using a 3Hp/2.2Kw motor on a 13amp plug expect trouble as if run for long things will get hot. If buying second hand at the lower end of the quality range then The safety of the pressure vessel (tank) MUST be considered. If there is no test on the tank, it must be considered as a parts only deal. HOW do I know ? Asked to repair an 11year old unit, the unloader/ cutout leaked badly so fit new, tried to run it, motor u/s, new motor £160, NOW it runs ! This unit was spotless and LOOKED like new. After a few seconds a small puddle appeared under the tank ! It had corroded through, a tiny pin hole. Customer unhappy and me £250 out of pocket as a new tank is costly.

I should have done a hydraulic test FIRST ! and condemed the unit , at that point customer would have accepted it and I would have got paid. Noel

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