Blast pot grit flow problems

[matchless_mike]

I have recently bought a 20g blast pot off Ebay and am using it with Sealey B/25KG bags of grit (0.2 to 0.7mm) along with a Clarke 14cfm 150psi compressor.

The problem I seem to have is that it appears that the grit does not always flow through the grit valve at the bottom of the blast pot - leaving me just blasting air ! Tipping the pot back and forth and trying to give it shake sometimes gets it working again. I have tried varyng the amount of grit in the pot from as little as 12kg but with no improvement. When I empty the pot I don't see any evidence of a blockage at the bottom - just the ball valve.

I do sieve the grit before use and let the pressure in the pot build up to over 100psi before use. Any suggestions/solutions appreciated !

 

[brightspark]

try taking the tee piece of the bottom of the ball valve . then regulate the valve see what flow of grit u get through it. NOT PRESSURISED OF COURSE

 

[rtbcomp]

Make sure the air is dry.

When you just get air close the bypass valve then

1) if air continues to flow the grit is not dropping to the bottom of the pot, it is sticking together and a hole has been "bored" down through the centre. Caused by damp and excess dust.

2) if the air stops, the outlet at the bottom is blocked. The buildup of pressure may free it and transfer the blockage to the nozzle.

Try reducing the pressure, 90 psi should be enough, I've used mine down to 40.

I start off with all valves closed, open the inlet valve and when pressure has built up open the bypass valve fully and then open the bottom valve VERY gradually until the correct mixture at the nozzle is achieved.

To shut down temporarily, close the bottom valve and when the hose has purged close the bypass valve.

To shut down completely as above but close the inlet valve and leave the bypass valve open until the pot has depressurised completely.

 

[brightspark]

does the blockages occur with a pot full of new grit or only after its being re used . u said u sieve it that gets large particals out and makes regulating consistent but do u sieve all the fine dust and grit out as well after use . as this tends to block the free flow through the regulator valve and stick in a clump

 

[matchless_mike]

Thanks for the info. Having dismantled things I found that damp and dust had caused a blockage just below the ball in the grit valve. What more can I do to stop moisture ? Add another moisture trap - say near the the compressor outlet ?

With regard to dust - I suppose each time I use the grit (Once only at the moment) there's more dust in the grit making the probability of dust blockages more likely. I suppose I will have to sieve the used grit for large debris and then use a fine sieve to remove some of the dust ?

 

[rtbcomp]

The trap on the pot isn't much good. The best system would be to have a regulator & trap near the pot and feed it with high pressure straight from the compressor. This means the air in the pipe will have chance to cool and will cool even further when the pressure drops at the regualtor. This gives the best chance for moisture to drop out.

I use a 1/2 inch Thorite regulator/filter, I haven't had much luck with Clarke ones.

You're right about the dust. As soon as the media sticks in the funnel when you fill the pot is a good time to sieve the dust out. I'm currently working on a sieving system, I'll publish it here when done, probably a week or two yet.

 

[papperbear]

I have recently bought a 20g blast pot off Ebay and am using it with Sealey B/25KG bags of grit (0.2 to 0.7mm) along with a Clarke 14cfm 150psi compressor.

The problem I seem to have is that it appears that the grit does not always flow through the grit valve at the bottom of the blast pot - leaving me just blasting air ! Tipping the pot back and forth and trying to give it shake sometimes gets it working again. I have tried varyng the amount of grit in the pot from as little as 12kg but with no improvement. When I empty the pot I don't see any evidence of a blockage at the bottom - just the ball valve.

I do sieve the grit before use and let the pressure in the pot build up to over 100psi before use. Any suggestions/solutions appreciated !

im a shotblaster have you strip down the bottom of the valve that controls the flow of shot it could beworn see if it is that could be the fault