Modification to Pressure Pot.

[rtbcomp]

I use crushed glass for blasting and while it breaks down easily it remains sharp. This means it's still useable when it reaches the consistency of flour!

However such fine media sticks in the pot. I found I could get it to feed better by slightly closing the valve 'B' in the diagram below.



This increases the pressure in the pot, but reduces the flow through to the nozzle and hence the blasting force.

So I reconfigured the plumbing as follows



I've found that by setting the regulator to 4-5 bar and adjusting the flow with the gate valve 'G' I get a much more even flow of grit and at a greater force.

Surging, where the grit comes out too quickly and blocks the nozzle, is almost eliminated which means I get more useful blasting from a full pot.

The ball valve 'B' cuts off the airflow so I can leave the gate valve set. Closing 'B' momentarily will clear any blockage at the lower valve 'L'.

Closing valve 'T' and opening 'D' de-pressurises the pot for filling. Leaving 'D' open during filling lets the air out as the media enters the pot, making filling easier.

 

[brightspark]

why have u moved the water seperator along the line in the second picture. now it only stops water to the pot and not down to the blast pipe . the first picture shows both been covered in the supply line

 

[brokenbiker]

what type of valve do you use for 'L' ?

 

[rtbcomp]

The trap is a filter/regualtor. I wanted to regulate the pressure in the pot independently of the feed to the nozzle.

There are water traps further upstream and I don't get any problems, even when the air is warm.

The valve 'L' is a bog standard lever operated ball valve.

 

[brokenbiker]

cheers. what did you make the pot from? would a gas bottle be appropriate?

 

[rtbcomp]

It was an Ebay special (Machine Mart sell them) I was going to make one but at that time they were so cheap it wasn't worth it.

Loads of people have made their own pots from gas bottles, do a search in this section of the forum.

 

[brokenbiker]

cheers. i already have a compressor that will run 6 bar, and a handfull of gates and valves so i shall get hold of a bottle and have a go

 

[500e]

Its late & had a hard day but what about the feed via B G this has 4\5 bar into media via L


Closing valve 'T' and opening 'D' DE-pressurizers the pot for filling. Leaving 'D' open during filling lets the air out as the media enters the pot, making filling easier.

 

[rtbcomp]

The pressure via B,G & L is greater than 4-5 bar, it's at compressor pressure. However it is acting on a smaller area (about 3/8" dia) than the 4/5 bar at the top of the pot.

The pressure at the top of the pot imparts a greater force on the media than the pressure at the bottom.

It's the difference in force on the media that forces it through the valve L.

Total Force = (top pressure x area of pot) + weight of media - (Pressure at bottom x area of lower port)

 

[500e]

Closing valve 'T' and opening 'D' DE-pressurizers the pot for filling. Leaving 'D' open during filling lets the air out as the media enters the pot, making filling easier.
Not talking about use, but filling if you have 3\4 bar injected at bottom with no pressure at top Puffffffffffffff goes the media? or am I still tired

 

[brightspark]

Closing valve 'T' and opening 'D' DE-pressurizers the pot for filling. Leaving 'D' open during filling lets the air out as the media enters the pot, making filling easier.
Not talking about use, but filling if you have 3\4 bar injected at bottom with no pressure at top Puffffffffffffff goes the media? or am I still tired

surely u would have to close b and t to de pressurise :

 

[rtbcomp]

Wakey! Wakey! You switch the air off before filling the pot.

Mind you, if you open D with pot 3/4 full and under pressure a great deal of media comes out very quickly!

This is a good way of freeing media that sticks to the sides. It's impregnated with air under pressure, releasing the pressure dislodges the media.

 

[rtbcomp]

surely u would have to close b and t to de pressurise :

That would work, but I have a main lever valve not shown on the diagram.

 

[brightspark]

That would work, but I have a main lever valve not shown on the diagram.

that answers that question then , it should have been shown as well

 

[rtbcomp]

Starting with all valves shut, I open 'T' to pressurise the pot, then 'B' to blast any stray media out of the hose. Then I slowly open 'L' to feed the grit into the airstream. Adjusting the pressure and 'G' to get the correct blast.

As the pot empties closing 'G' or increasing the pressure ever so slightly will compensate for the reduced weight of media without noticeably affecting the blast.

To shut down I close 'T' then 'L' wait for the hose to empty and the close 'B', finally opening 'D' to depressurise the pot.

It's important to empty the hose, otherwise when you start up a big wodge of grit blocks the nozzle.

 

[mm289]

Really useful, thanks

Just about to start blasting a chassis so might make these mods as I get fed up with having to keep unblocking every 5 mins on the bigger jobs!

MM

 

[500e]

Yep B &T

 

[dannyp]

theres my modifyed ebay blaster, much less complicated.

1 valve turns the main air supply on and off.
1 valve regulates the grit

all the air goes throught the filter pulled it off an underfloor hydrovane on a iveco van, when in use a lot of water is expelled from the drain pipe on top.

air goes from the filter to tee fitting most of the air goes straight across the T down to the mixer T at the bottom so it has a quite straightforward run in 5/8th pipe, the pot is pressureised by smaller pipe comeing off the T and it has a restrictor fitted so going into the pot it's only 1/4 "

this measn that when you close the MAIN air supply whilst the pot discarges though the nossel it also gives much bigger pressure differance across the grit metering valve to clear it should it block.

made it from a near useless ebay blast pot and some scrap in a few hours the bits i had to buy tho were the blast nossel and fitting for it to the balst pipe and from the blast pipe to the blast pot. the blast hose itelf is knackerd hydralic pipe, nossel was most expensive bit at £90

 

[brightspark]

i scored my blast nozzle and hose with fittings for 40 quid and a spare 6mm nozzle for 15 quid

 

[rtbcomp]

theres my modifyed ebay blaster, much less complicated.

1 valve turns the main air supply on and off.
1 valve regulates the grit

.........

That's pretty much like the standard pot, but without a valve in the pipe down to the mixer. As that valve is usually fully open your setup isn't that much different to standard.

As I explained in my original post my modification allows the pot to be used with VERY fine media, the standard setup doesn't. I've been using this most days since I did the mod and it has made a vast difference. I get much more use out of the media than I did previously.