DIY Pressure Pot

brightspark · Nov 1, 2009

m@tt said:
Excellent

so what would you recommend for the pipework?

The ones in your pic look like they might be larger than 1/4"?

bsp is measured from the inside standard threads on bolts ect are measured on od so bsp is misleading on its size :laughing:

rtbcomp · Nov 1, 2009

I'd go for 3/8 bsp and 14mm blast hose, I've used 1/4 fittings and 10mm blast hose and it's not upto much.

Also the wear on the hose is proportional to its diameter, the amount of grit delivered is proportional to cross-sectional area, ie diameter squared.

brightspark · Nov 1, 2009

the 90 cfm i used had half.inch blasthose with 6.omm nozzle any larger and the grit bounces around in the hose loosing speed .its not critical mind i use 7/16th bore thickwall blasthose fine on 3mm nozzle

M@tt · Nov 1, 2009

so would these valves be suitable?

http://cgi.ebay.co.uk/Ball-Valve-3-...emQQptZLH_DefaultDomain_3?hash=item19aa5669aa

brightspark · Nov 1, 2009

m@tt said:
so would these valves be suitable?

http://cgi.ebay.co.uk/Ball-Valve-3-...emQQptZLH_DefaultDomain_3?hash=item19aa5669aa

verry and the price is rite :laughing:

M@tt · Nov 1, 2009

excellent, i'll get ordering

M@tt · Nov 1, 2009

in terms of the rubber blast hose i can get barb/tail fittings in either 3/8" or 1/2" is 1/2" (12.5mm) going to be the best to go for?

M@tt · Nov 10, 2009

well i had a little go tonight an the blast pot, i received the fittings i ordered and then promptly realised i'd miscalculated exactly what i needed so i've had to order some more, doh!!

any way heres a few little pics

Having read some other posts and based on cost and the fact that its will get ocassional use rather than everyday hammer i'm going to use some reinforced PVC hose for the flexi pipe and some 3/8" PCL hose tails as a nozzel, they'll be cheap to replace if and when they do wear

brightspark · Nov 11, 2009

your getting there

best pipe to use would be rubber reinforced airline .pvc tends to stiffen and go brittle . if u havent got water seperator get a 1/2 inch one from machine mart there 16 quid with reducers included . tungsten jet can be bought from pkr trading .the tel number is on earlier thread :carry on the good work

3mm nozzle required 3/8 too big there only 14 quid a must realy

malcolm · Nov 11, 2009

Some of your welding looks a bit iffy. They look cold and too big, and with MIG there's a risk the weld will not penetrate when it's too cold, instead sit on the surface.

I like to consider failure modes when deciding how (or if) to tackle a job. Pressure vessels can have fairly nasty failure modes involving death so I don't get involved with them at all. They are difficult to test on a DIY basis and are prone to fatigue so ought to be perfect to start with.

Personally I'd buy one of the Chinese Machine Mart ones. Failing that can it be installed in a wire cage so that it limits some of the potential injury if it goes pop. Even 90psi can send things a long way

eil · Nov 11, 2009

Did you get a leak with the mig weld and go over again to try and seal it but the leak moved somewhere else and so on? I know they are mig welded when made but if you have an arc welder I would have personally used stick, and put it in something more solid than a wire cage.

M@tt · Nov 11, 2009

the welds were does with my Clarke 160TE with it set to "3" and "Max" and wire speed up nice and high, i went round everything a couple of times to make sure it was well fastened and it all certainly feels pretty well stuck together although its a bit hard to properly check penetration but the whole area was glowing nicely which i thought would indicate the thicker material was getting good penetration.

Might sound daft but if you're welding dissimilar thickness materials together is there any benefit in heating the thicker section up with a blowtorch first to aide penetration?

brightspark · Nov 11, 2009

adition

if u want to pressure test a tank fairly safely and simple. fill it 2 thirds.full with water then pressurise to about 150 psi if it does let go there isnt the.volume of air to do damage thats how they hydraulic test steam boilers .another thing is i do. test welds on things even if it looks a bit rough weld tubes to flat plate and angles give them the hammer test if it bends its ok if it snaps it isnt

malcolm · Nov 11, 2009

It's not pressure testing I'd be worried about - fatigue will be the risk. Closest thing on here that we normally see are the photos of pipe welding, and you can see how much attention to detail to corrosion and fatigue they put into welding those things.

Welding round and round again will not necessarily make the weld stronger. What about cooling stresses? That's one reason why you don't see that technique mentioned in books.

Shox Dr · Nov 11, 2009

brightspark said:
your getting there best pipe to use would be rubber reinforced airline .pvc tends to stiffen and go brittle . if u havent got water seperator get a 1/2 inch one from machine mart there 16 quid with reducers included . tungsten jet can be bought from pkr trading .the tel number is on earlier thread :carry on the good work 3mm nozzle required 3/8 too big there only 14 quid a must realy

Are you sure. Any amount of air in a vessel while been tested is a big no no.

I built this Blast pot a few months ago, and tested it to 250psi with water and a high pressure pump. No leaks and Im still here.

All TIG

eil · Nov 11, 2009

If you didn't have your tig Shox, which method would one use.

Shox Dr · Nov 11, 2009

eil said:
If you didn't have your tig Shox, which method would one use.

Either works MIG (350Amp) not that you need that much but it is a very nice machine to use

Or stick using my TIG box on MMA DC

eil · Nov 11, 2009

Its this cold start problem with the mig though as m@tt is saying would you heat it up with a torch first or start welding away from the joint and work in, or just go with the mma as I would personally prefer. Do they use mig on pressure vessels out on sites or is it just tig and mma.
Regarding the pressure testing, receivers are hydraulically tested with water and then pressure pumped up to strength test, then reduced for leak test, I test air con systems with oxygen free nitrogen as you cant have moisture in the system, that strength test can be as high as 625psi and leak test for 24hrs at 483psi. just wondering why you cant fill your receiver up with water and then pressure test with compressed air to whatever test pressure thats stated on the rating plate, I'm sure someone will enlighten me.

M@tt · Nov 11, 2009

i fitted the filling socket and cap tonight, the welds were a little neater tonight

classic2cv · Nov 12, 2009

Shox Dr said:
Are you sure. Any amount of air in a vessel while been tested is a big no no.

I built this Blast pot a few months ago, and tested it to 250psi with water and a high pressure pump. No leaks and Im still here.

All TIG

any more photos of your blast pot :cool:

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