grit valves for cheap pots

  1. brightspark

    brightspark Member

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    yarm
    using ball valves to meter the grit is a bit hit and miss and prone to regular blockages :(namely because of its design and iregular grit size it only takes one larger particle to end up in the orifice and everything stops . even the slightest of moisture kills it off . making a flat sand valve cures the problem no end ;)the grit falls through on to the metering valve which sits slightly higher than the outlet. the lever is turned untill the corect amount falls through.3/8 bsp fittings are used giving a good clearance for the grit to fall through without clogging up/. any iregular media falls to one side of the valve and just sits in the bottom cup and doesnt stop the flow . even with moist air it rarely blocks up and there well worth making heres mine .its fitted to the small pot the larger pot i have will be fitted with the same sort of valve another good help is a cooling cylinder next to the pot and i use c couplings in stead of the eurofittings that are still restricted
     
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  2. rtbcomp

    rtbcomp Moderator Staff Member

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    Very good. You ought to get into production, I reckon they'd sell on eBay.

    What I find happens with ball valves is that they slowly clog up, the stream of grit slows down, so you open the valve a bit and do some more. Eventually the valve is fully open and the stream stops, or more likely the blockage breaks free and blocks the nozzle!

    It's worse the more dust you have in the grit, brand new grit is usually OK.

    I did try a gate valve in order to get more precise adjustment, but that doesn't allow you to cut off the grit quickly. I then tried a ball valve after the gate valve, but that didn't work at all.
     
  3. rtmroger2 pre-moderated

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    Asia
    Thanks for the post
     
  4. brightspark

    brightspark Member

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    blastpot valve

    new home made grit valve for the larger pot
     
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  5. Dcal Member

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    1,271
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    Antrim Northern Ireland
    Found this through google and not the site search function, but no matter, hope you don't mind me copying.
     
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  6. brightspark

    brightspark Member

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    made another out of cast aluminium its easier to machine and make than the steel ones
     
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  7. scottmk1

    scottmk1 Forum Supporter

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    Fancy making one for me?
     
  8. brightspark

    brightspark Member

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    rather time consuming but worth the effort. if you have a lathe and get a half inch bsp tap that's all that is required to make them and a blob of weld on the slide valve I can find out how much me mate would charge for the 2 castings if you didn't want to maker them out of steel
     
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  9. scottmk1

    scottmk1 Forum Supporter

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    Ok, any advantage using aluminium? I do have a lathe but I'm in the middle of putting it back together, so could make one after that it complete.
     
  10. brightspark

    brightspark Member

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    only advantage is its easy to machine from the castings no different if you get some steel it just takes a bit longer to make
     
  11. scottmk1

    scottmk1 Forum Supporter

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    Ok, I'll leave you in peace and make a steel one when I get the lathe finished.
     
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  12. slim_boy_fat

    slim_boy_fat Forum Supporter

    Patent pending? ;)
     
  13. Dcal Member

    Messages:
    1,271
    Location:
    Antrim Northern Ireland
    @brightspark hope it's OK to resurrect and hijack your thread?
    Your work on the grit valve was certainty the inspiration for me having a go at this.

    Here's my version so far.
    Started messing about with it after my earlier post in this thread.

    Dimensions, as always, are based on what's in the scrap pile.
    I remembered I had a bit of 72mm tie-bar kicking about so dug it out to see what it's like to cut and machine.
    They are usually a similar grade to re-bar but this is old (70 or 80 years?) so it's anybody's guess.
    It seems fine to work with.

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    Sliced a couple of bits off with the band saw

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    Bit of a variation on the design.
    I don't know if it's necessary, or if it will improvement it, or if it will even work but I machined a funnel into the lower part of the valve to see if it improves the flow of grit.
    I'm also going to see if I can make it in 2 thicker bits and leave out the middle spacer.

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    Starting to get to grips with this 4 jaw clocking malarkey.
    Next to no step when I turned the blank around in the chuck to machine the other end.

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    I went for a 10mm orifice for the grit, but that seems big so might make a smaller one.

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    That's it for now, another evening's messing should see if the prototype works.
     
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  14. brightspark

    brightspark Member

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    26,853
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    that's looking quite canny. the 10mm outlet should be ok as the flat valve covers it when closed and shouldn't flood the outlet when partially opened to either run kiln dried sand or grit the fittings on my smaller pot are 3./8 bsb outlet and I think the top one from the pot in to it maybe half inch bsp . to be honest I wouldn't have made the top a cone and left it flat maybe no more than 10mm higher than the flat adjusting plate as it will allow the grit to pile up in the chamber and clog the outlet :) other than that its getting there :) keep us informed with piccies and progress
     
  15. Dcal Member

    Messages:
    1,271
    Location:
    Antrim Northern Ireland
    I was thinking of installing it the other way so that the grit enters through the flap and out to the blast pipe through the cone.
    As I've said I'm just guessing here and had assumed that once the grit entered the valve it should pass straight into the air stream in the blast pipe and not stay in the valve at all.

    Only one way to find out.
     
  16. brightspark

    brightspark Member

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    Location:
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    its up to you but the ones ive made were copied and measured of the the original Clemco minipots and I have used them for over 35 years .the flap needs to be on the top and the grit falls down the tube the other way on it will just pile up and clog the valve . the valves sold by centurywise for about 125 quid are identical. there tried and tested design and cant be improved upon
     
  17. Dcal Member

    Messages:
    1,271
    Location:
    Antrim Northern Ireland
    O dear!
    I think I've misunderstood the design.

    I thought the grit came through the regulator flap from the pot and then into the lower half of the valve and on down to the blast pipe.
    If I understand you properly (and from looking at your assembled valve again) the grit comes into the valve, fills it and then is dispensed through the regulating flap and down the blast tube.

    No matter, it's not the first time I've done something arse about face and it's only a bit of fun, so I might as well finish it now and see if it works at all.
    Bound to be better than the poxy ball valves and it was a good bit of practice on using the lathe.

    I'll post a few photos of the finished article later.

    If it doesn't work I'll start again.
    At least I'll know how not to do it.
     
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  18. brightspark

    brightspark Member

    Messages:
    26,853
    Location:
    yarm
    just alter it now and it will work fine machine the dome off and narrow down the orifice otherwise it will all; fill up and wont operate .once I have regulated mine it will run all day without touching the lever providing the sand or grit is new and uniform in size and you control any water in the line
     
  19. Dcal Member

    Messages:
    1,271
    Location:
    Antrim Northern Ireland
    Just got the metering valve finished and assembled for a dry run.
    it looks very different to brightspark's and works upside down I think (if it works)

    Instead of tapping the valve for the BSP fitting, I just welded steel fittings into the inlet and outlet.
    I also welded a boss to where the metering valve spindle foes into the body to give it more support (probably overkill but why not)

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    I drilled the holes too close together so needed to take a bit off the barrel.

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    Drilled and tapped the body for M6 bolts and decided to make a new smaller 8mm grit inlet orifice, but this time I have it so that the inlet orifice can be changed without dissembling the whole valve (like a carb jet)
    it's made out of a M16 A4 counter sunk set screw that I turned down so it would fit inside the inlet BSP barrel.

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    Everything else was straight forward.
    Flap valve made out of a bit of stainless wall tie and a 10mm bolt.

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    The finished components.
    I had all the bits laying about so didn't have to buy a thing.

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    Dry assembled

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    And on the pot

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    I don't know if it will work (bit late to be blasting) but the grit does flow and can be regulated and turned off with the lever.

    I've a few more mods to make to the pot (raising the height above the ground so the new valve will fit under it) and I'm thinking of installing a big bung to the underside so I can empty it easily if I want to change grades.
     
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  20. brightspark

    brightspark Member

    Messages:
    26,853
    Location:
    yarm
    it will sort of work but wont be anywhere as good as if the valve is the proper way round and probably clog up :)
     
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