Struggling with blast pot

[Pdutton]

Firstly - congratulations on a great site. Helped me teach to myself to weld last year, enough to do minor repairs on my landrover.

I've just bought myself a 10g pot to do all the small bits on my landrover and then the chassis. But I am really struggling. I know That my compressor is not up to the job and intend hiring one to do the job properly, but I would have expected better results with what I have. The compressor is 2.5hp 9cfm.
I am using jblast superfine and a 2.5mm nozzle.
I can blast ok for about 10 seconds with the pressure at around 7bar. But as soon as it drops to 6bar the flow of grit stops and air pressure reduced dramatically and the hose blocks. Removing the nozzle and clearing the hose brings the pressure back.

Is it simply a case of the wrong compressor Or is there something more fundamental I am dong wrong. I am keeping the mixing valve closed until pressure builds up. It's almost like there is too much grit in the for the air to move.

Reading some of the posts here I like the idea of a 6mm nozzle and using a road compressor to get better coverage when I come to the chassis. But am reluctant if its not a compressor issue I am having.

Thanks.

 

[brightspark]

Firstly - congratulations on a great site. Helped me teach to myself to weld last year, enough to do minor repairs on my landrover.

I've just bought myself a 10g pot to do all the small bits on my landrover and then the chassis. But I am really struggling. I know That my compressor is not up to the job and intend hiring one to do the job properly, but I would have expected better results with what I have. The compressor is 2.5hp 9cfm.
I am using jblast superfine and a 2.5mm nozzle.
I can blast ok for about 10 seconds with the pressure at around 7bar. But as soon as it drops to 6bar the flow of grit stops and air pressure reduced dramatically and the hose blocks. Removing the nozzle and clearing the hose brings the pressure back.

Is it simply a case of the wrong compressor Or is there something more fundamental I am dong wrong. I am keeping the mixing valve closed until pressure builds up. It's almost like there is too much grit in the for the air to move.

Reading some of the posts here I like the idea of a 6mm nozzle and using a road compressor to get better coverage when I come to the chassis. But am reluctant if its not a compressor issue I am having.

Thanks.

a 14cfm comp is the bare minimum and even that cant keep up with a 3mm nozzle . the presure needs to be about 90 psi constant it will work on less but as the pressure drops the blast pipe fills with grit hence the blockage in the jet , the max grit size for the 3mm nozzle would be j blast superfine .if u did use a 6mm nozzle u would have to upgrade the pipework and fittings to half inch bsp and use a 15mm blast hose if u need more info pm me

 

[rtbcomp]

How have you got the valves set?

Open the top & side valves fully and gradually open the bottom valve until a barely visible stream of grit can be seen.

I've used these pots down to 40 psi, although it didn't shift much paint at that pressure! As BS says you need 14cfm (3hp) min to get any real use out of one of these pots.

 

[Pdutton]

Thanks for the quick answers. I've kept the mixer valve closed until pressure builds up, with the top valves fully open, then open the mixer valve about 1/2 way. As soon as the pressure drops the pipe fills.

Just been out to find a compressor the local hire company do a 80cfm one, but they said someone else tried it for blasting and it wasn't up to it, they needed 100cfm.

 

[rtbcomp]

14 cfm will work that pot, the hire shop was probably talking about building type blasting. I use the 20 gall version day in, day out with about 23 cfm from 2 compressors, although they do run continuously.

Once the pressure has stabilised with top & side valves open it shouldn't drop when you open the bottom valve, in fact it will take less air when media is added to the airstream.

How full is your pot? It's best to start at about 3/4 full.

Don't open the mixer valve in one go, as I said open it gradually.

 

[johnzx6]

hi,i'm just starting out to you won't go far wrong
listening to these guy's,best thing joining this site.
i had the same problem's i turned the pressure down
a bit and opened the grit valve about quarter open,
it's a bit slower but works and a found keeping the
pot topped up helps.
cheer's,john.

 

[merckx2]

It's so important to keep and eye on the nozzle size, if you're using the ceramic ones that come with the pot they do wear relatively quickly which will have a massive impact if the compressor isn't that big.

*****If a 3mm nozzle wears to a 4mm size the air flow required to maintain the blasting pressure increases by a massive 70%. *****

A tungsten carbide nozzle on ebay would be a good investment.

I'm getting good results with a 3mm nozzle with J blast superfine, 14cfm compressor. I do have to pause and let the pressure build up all the time but it's bearable with the compressor running constantly but the rust removal is quite good.

When I ignored the nozzle wear and it opened up to over 4mm the perormance was so slow.

If you don't have a lot of grit in the pot you also need to keep shaking it as a hole will form through the grit leaving you blasting just air.

Also, If you're opening and closing the valve at the nozzle it will wear relatively quickly and you'll find it'll start leaking your precious air when it's closed.