Vacuum Pump Build - Advice please...

[J.F. Custom]

Hi All.

Well, I've had all the equipment to build one of these for some time and am wanting to cross it off the list, not to mention, put it to use. I've got one of the US Thomas pumps care of Micheal some time ago, as well as an EVS kit from Joe at Veneer Supplies.

Now I have a problem. The reservoirs call for that PN18 (Schedule 40) rated PVC pressure pipe - though Kim stated PN9 should suffice. I had heard this was expensive but until today, had not considered just how expensive. I was quoted by Reece Plumbing at about $50 per meter for PN12 rated 100mm pipe. Expensive, but not undoable, until I got the price on the end caps to suit; @ $25 each. Four required brings that total to $150, before the smaller sub/reserve/free air reservoir is factored in. I'm guessing $200-220 odd all said, potentially much more if I requested the PN18 instead - not a price I had factored into the kit build and surely cheaper alternatives are possible.

So unless Kims' mates are feeling thirsty and generous once more ( ), I'm looking at alternatives to this set up. I saw that Micheal had set his up with a compressor tank and have seen photos of same on the joe woodworker site. I was even donated an old dead compressor for the use of its tank. Unfortunately though, it is very old and not in the best condition. I'm concerned about internal corrosion and on top of that, I'm not sure what style of compressor it was but it is nothing like my larger tank. It has about six tapped holes of various sizes that would need to be plugged up before I could adapt one for use. All in all, not worth the effort I'm thinking.

So thinking some more, I considered empty fire extinguisher tanks, scuba tanks or LPG gas cylinders. Not sure where I'd get the fire extinguisher or scuba tanks so first port of call was the gas cylinders. Checked bunnings today and they have a few sizes. The largest they've got is a 9KG bottle for only $36, but the sizes range from $20 to $40 odd. The 9KG cylinder has a 22 litre capacity. By my calculations, which could be wrong I admit, the PVC reservoirs called for would provide only about 3 litres capacity each, giving a rough 6 litres total.

My questions to you all with more experience in this field therefore are these - Given that one tank provides far more capacity than both PVC reservoirs, would I just need one main cylinder or would having two smaller cylinders be more advantageous with respect to the way the system works with it's back up vacuum reserves? On top of this, should I also get a small say 1KG cylinder for the "temporary free air" reservoir? So potentially three tanks (two large and one small) or two tanks (one large and one small) do the job? Good idea or ??

Any other comments, alternatives, suggestions or even sources for PVC pressure pipe offcuts would be welcome. I'd love to get this jig completed.

Thanks,

Jeremy.

[Kim]

Jeremy,

I see no reason why a single 9kg gas cylinder would not work. You would still need a small 40mm PVC bypass tank or something similar to allow the pump to come up to speed each time it kicks in without working against the stored vacuum in the main reservoir, but a single main reservoir would be just fine.

The two PVC tanks of the original Joe's design work in tandem, the idea being to reduce the over all size of the finished vacuum station. That design also keeps the weight down yet provides the required volume. I think it was Allen who put together a unit with a pair of aluminum tubes and I think he used shop made end caps from nylon cutting board material. That was a great way to achieve the same results as Joe's design and it looked pretty swish as well. From memory Dom used an old LPG tank for his reservoir and has it plumbed in as a permanent fixture under his bench, that design works great too.

Some have suggested that even 'down pipe' grade PVC would be fine. My main concern with that is that the walls are just too thin. They would be sucked inward like a semi collapsed lung creating a reduction in the tanks volume. This would cause the pump to shut off earlier than it should and then as soon as you applied any vacuum, the walls would pop out again thereby increasing the tanks volume and resulting in a reduction of vacuum pressure. I think in the short term this effect would result in the pump stopping and starting far too often. It would be forced to run in short burst in effort to maintain the setting of the mac valve. In the long term would probably fatigue the PVC until it either collapsed or ruptured. It would probably also reduce the longevity of the pump itself.

Bottom line is that I think you just need a tank of some kind with rigid side walls. Yes I did use class 18 on my unit and got the pipe and end caps thrown in for the price of a carton. But now the unit is built, I believe you could get away with using class 9 and most certainly class 12. The only issue is that 'all' PVC caps are made to a class 18 standard so that one fitting will work in all class applications, so it certainly 'is' a bit exie regardless of which class pipe you use if you need to buy them. The other issue is that the brass fittings in Joe's kit are simply not long enough to reach between the centres of two side by side class 18 end caps. The caps are just too thick in the side wall, so even if you do buy them, you then need to turn them down on a drill press or lathe so that when they sit side by side, the fittings can link as per Joe's design. Either that or you opt to pay out for more brass fittings.

All said and done, if size and weight is no big issue, then the 9KG gas bottle option is looking real good

Cheers

Kim

[Dominic]

Hey Jeremy, I used a 20l gas tank as my main and a small 1l gas tank as the buffer. I had both here but bunnings has them also and they are cheap and already threaded. I easily found a fitting that went from the tank to the pump fittings for both tanks. Works great. I have it all mounted on a shelf behind my workshop wall with fittings and taps installed on the inside for connecting jigs etc.
Cheers
Dom

[jeffhigh]

Whatever you use, at least it is not catastrophic if it fails since it will just collapse rather than explode.
Always used to have trouble explaining to contractors why they could not pressure test the new pipeline with compressed air rather than water.........

[Allen]

I used an old air compressor tank that I rescued from the tip shop. I think it's around 30 litres.

Was the princely sum of $10. The earlier version I made was leaking more than I liked and I sure do like the extra capacity of this version. Micheal did the same thing with his as it comes with wheels and handle, so easy to drag around the shop if the need should arise.

[ozwood]

Another Idea would be expired Fire Extinguishers, they are good Pressure/ vacum vessels!

[kiwigeo]

Another Idea would be expired Fire Extinguishers, they are good Pressure/ vacum vessels!

Careful....often extinguishers get chucked because they're corroding around the bottom. The things are often left sitting in puddles etc for years.

[J.F. Custom]

Thanks for the replies gents.

Just the info and feedback required. Given the expense of the PVC and the limited capacity, I'll go with the LPG tank.

Kim - thanks for the "why's" about the PVC choice for Joe's kit. I couldn't think of why the second main tank was 'necessary', but I am no expert so figured there may be something I was missing. I'll just get one larger main tank and a mini tank for the buffer.

Dom - good to hear you made the same choice and already have yours operating on it. I'll have to find the extra fittings I'll need though - may not be as easy out where I am. Piping in from outside is worth investigating too. I have very, I mean very limited space in my shoebox... I mean workshop.

Thanks Jeff, that's a good point and I'm glad you were there to advise them

Allen, interesting to hear your update - I won't take the alloy tube bread board option then The compressor tank idea does appeal as it has even greater capacity and the convenient wheels. Problem is, the old one I have I don't trust and I would not know where to get another in better condition. I don't think you can buy them like this so it would be like you, checking tip shops etc. I think for the price and convenience, I'll just go the LPG tank.

Ozwood, yep I thought of those as I mentioned above but they are not as easily accessible for me and then you have the concerns Martin raises, similar to my thoughts on the old compressor tank I was given. At least the empty LPG's at bunnings are unused and therefore should be in very good nick.

Thanks again.

Jeremy.

[Allen]

Micheal bought a cheap compressor from Bunnings. Chucked the motor and kept the tank. Didn't even need a paint job then.

[Dominic]

Here is my setup. So the shelf is right behind the wall and next to my main bench. The switch in the middle of the powerpoint in the second picture turns the pump on. And I have 2 line outs with taps but add up to 2 more if I wanted. Something I would change is to mount the vac gauge on the ply plate so I can check and adjust from inside if needed.
Dom

Vac 002 (Custom).JPG

Vac 001 (Custom).JPG

[J.F. Custom]

Hey Dom.

Couple of questions if you don't mind.

It looks in your picture as though you have kept and utilized the original gas tank fitting as opposed to plumbing direct into the tank. Is that observation correct? - it is hard to see precisely in the picture. Any reason for this aside from convenience?

Where did you obtain your adaptors for this and other fittings from? I didn't check Bunnings while I was there - a three year old doesn't make for relaxed rummaging of brass fittings The gas fittings appear to be left hand threaded, so my local hardware is probably out as they are likely to stock the more common right thread plumbing fittings only.

I went ahead and got a small 1.25kg tank as well as a 4kg (10.3L) tank for the main reservoir. Despite only a $2 difference, I went with the 4kg over the earlier mentioned 9kg due to limited space in the workshop. I think the 4kg should be enough but if not, well $36 to go to the 9kg instead is not a major issue. However, as I said above, the 'gas' fittings are left hand thread. The threads direct into the tank are right hand though, however I believe the tap fitting supplied has been glued in place as well - probably a loctite or similar product making removal a pain.

Not sure if I would be better off trying to remove this loctite fitting somehow and plumbing direct, or going further afield and sourcing some left hand thread adaptors which is why I ask how did you adapt yours and where did you find the bits required?

Thanks in advance.

Jeremy.

[Dominic]

Hey Jeremy, I found the fitting in bunnings I think. One end fits the outlet on the tap and the other end my fittings. I might have found it near the camping stuff and not the gas section. I was surprised to find it and had thought I would have to take the whole tap out as you are thinking. But this made it real simple. So they do exist. Here is a pic. Dom

Pump 005 (Custom).JPG

[J.F. Custom]

Sweet, thanks Dom.

The picture helps heaps - thanks for the extra effort. I have exactly the same gas fitting on my tank, so I'll look for the same adaptor next time I'm in the vicinity of Bunnings.

Cheers mate.

Jeremy.

[Allen]

Any Hose Doctor or similar business will have a huge selection of this stuff on hand. I took in the fittings I needed to adapt to and in a few minutes they had me all sorted out. Even thought of things that I wouldn't have until I was back home and realised that I missed something.