High pressure air pump

[wimmetParticipant @wimmet]

Dear All,

I want to make a high pressure small volume air compressor suitable for charging my sons PCP air rifle. Pressure is approximately 300Bar.

Does anyone know of any designs that can be made in a model engineers workshop.

Regards Geoff

[wimmetParticipant @wimmet]

[John Wood1Participant @johnwood1]

Hi Geoff.  I think it very doubtful that you will be able to make a compressor to deliver that sort of pressure, apart from the stringent mechanical and valving requirements, those pressures are scary to work with. Dont forget that you would also need a good particle filter as well as very efficient moisture traps so that you don’t introduce moisture into the weapon.  A normal PCP actually only needs up to 200bar for charging so that should lessen your requirements a bit. Just for information 300bar is over 4300psi

 

To be honest, by the time you have sourced a design, if one exists, then got hold of the necessary components etc, then put it all together, is it really worth it when you can buy a new, 3litre 300bar diving cylinder, with hose and guage for around £180? and that only costs around £5 to have refilled.  Depending on your weapon you should get several fills before the pressure reduces to low levels with a 3litre bottle.

 

In case you were wondering, I own a gun shop and we have a German compressor to do the job (around £2000)

 

Hope this helps

Regards,  John

Edited By John Wood1 on 02/07/2010 16:27:28

[Richard ParsonsParticipant @richardparsons61721]

 

With my old Webley Axsor I bought a hand pump. It was about £40. To make one you would need about 600-700 mm of 25-35mm thick wall hydraulic tube. You will have to design the top guide, piston and valves your self. The pump shaft is 12-14mm solid rod and the ‘T’ handle is equally rugged. The bottom of the pump with the foot rests was also steel, with a 250 bar pressure gauge and had a ‘blow down’ valve to depressurise the system and get the gun off.

To use the pump you kept your back and arms straight and bent your knees letting your body weight do the work.

Edited By Richard Parsons on 03/07/2010 11:36:41

[John Wood1Participant @johnwood1]

That’s interesting Richard, a pump is certainly a much better option for home making, I presume the seals needed were easy to source and also the pressure guage.  Anyone contemplating such a build would do well to cost it out first because you can buy a decent new one 

for around £140.

 

Also dont forget to add particle filtration and moisture traps,  the last thing you need is to introduce moisture into the rifle.

 

Cheers

John

[Richard ParsonsParticipant @richardparsons61721]

 

Hi John,

The pump its self was rather like the old fashioned motor car type tire pump but much more solidly built. There was a simple water trap in the base of the pump and an in line filter.

The piston was sealed to the cylinder walls by ‘O’ rings and moved on the pump shaft closing off the inlet valve closing it against an ‘O’ ring.

The filler valve on the gun’s air chamber was sealed by two loose O rings which were compressed by air pressure.

I think it could be made in the normal workshop for about £40 or less, but I do not think you could do it with a mini-lathe.

Regards

Dick

     

Edited By Richard Parsons on 08/07/2010 12:15:41

[John Wood1Participant @johnwood1]

Hi Dick,

 

It’s certainly worth a go and should be quite feasable.  The main pump tube diameter would be about 28-30mm OD and would need to be fairly thick walled and seamless, length about 52cm should be about right.  I would probably use a block of ali for the base in which you can fit the pressure guage, bleed screw, air filter and hose output connector as well, of course as the main pump tube.  A simple tee handle fits on the other end and the whole would be mounted on some kind of metal plate which you stand on to stop lifting on the up-stroke.

 

You would need a high pressure hose with (probably) a 1/8BSP female threaded standard high pressure coupler to connect to your rifle’s filler connector, in your case a brass probe with two o-ring seals but as Geoff didn’t specify the make he will no doubt have the correct connector. The other end of the hose usually has a 1/8BSP male thread to couple to the pump.

 

Use a good quality silicone grease on the o-rings and, provided there are no leaks, you should be away – good luck anyone who has a go.  If you need fill adaptors and pressure fittings then try Googling for ‘Best Fittings’ on the web, they can be expensive but have lots of bits available.

 

I agree a mini lathe would probably be pushing it somewhat.

 

All the best

John

[TerrydParticipant @terryd72465]

Hi John,

 

I have a normal workshop compressor and have to evacuate quite large volumes of water from the tank after use. How would you suggest filtering the moisture out of the large volumes of air compressed by this high pressure pump?

 

Terry

[MSPF.Participant @mspf]

Hiya Geoff, I am about to start making a new PCP hand pump which will be fitted mechanically to pump HPA to fill my airguns instead of all that heaving and sweating. (In this weather).

If you google or use You Tube to ask 'How to build a PCP pump' you will see at least two designs that fill air rifles or scuba tanks.

Not pretty but they will do the job. John is correct HPA is dangerous but so is electricity, so like most things in a workshop, carelessness can get you hurt or worse. Safety is the responsibility of every engineer no matter what level they work at.

I suggest you have a look at the hand pumps available on the market. Hills or FX are reported to be good and expensive too. The tube is fairly easy to find and the seals. You can build one fairly easily and material like 'High pressure hoses' are not expensive unless you buy them from a gun shop. (No offense John but I find the prices in the airgun industry to be a complete rip off).

You only have to look at the HPA gauges the like of AA or FX put in their air rifles, they are basically expensive inaccurate crap. You don't have to believe me, just look on You Tube about how to replace one of their gauges and you will see for yourself the kind of expensive crap they foist on us.

So Geoff you can build a hand pump and with a little thought can turn it into a mechanical compressed air filler, not a huge compressor and it must be watched but it can be done Geoff and with a mini lathe too. In fact Geoff I no longer buy my airguns from the 'Cartel' but make my own. Courtesy of Mr H. M. Buckley and his book 'The Modern Pneumatic Airgun'. The only thing I don't make are the rifled barrels but there are plenty of spare used barrels knocking about.

HTH. Mike

[JonParticipant @jon]

I never ever needed a book to make a total one off air rifle down to each screw, big difference and still lead the way 24 years on after learning the hard way. Anyone can copy what they cant do is figure it out.

The Buckley book is based on 30 year outdated primitive stuff ie the Rentokil Daystates from mid 80's.

What no ones mentioned is rated pressure ie up to 200bar should withstand 300bar or better. Not even certain manufactured air rifles do that some blow at 235bar. There are some that can be topped up to 300bar ie Ripley and old Walther LG200/300 but reg will pack up.
Heres a 200bar cylinder I didn't expect to take 300bar, and the gauges are inaccurate. **LINK**

To even make a pump it will set you back not only in materials £40? but guage £7 to £70, hose £25 and quick fills £20+ and wont be too much short of buying from a shop around £140 tested and made for the purpose. Even then face the constant music of dispersing hot air on to filler valve and burning out. Even seen knock open valves burn due to using pumps because of the short bursts of air creating heat more than from a dive bottle. Forget whats its called but the prototype electric Daystates used tell you the temp within tube.

There are high pressure compressors petrol, diesel and electric non cheaper than around £1350 fo r intended minimal use.

Buy a bottle and be done with it £4 to £6 a fill costs more in wear and tare getting there. Luckily must be 12 within 20 mile.

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