problem with pressure blast cabinet

  1. Keithedw Member

    Messages:
    34
    Location:
    Wirral
    I have a large pressure blast cabinet the problem that is happening is that media is returning back into the valve at the back and jamming the valve ......question is shoud there be a non return valve to stop media flowing back up ?

    cheers Keith
     
  2. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    What make/type is it? A few photos would help.
     
    brightspark likes this.
  3. Keithedw Member

    Messages:
    34
    Location:
    Wirral
    Its a Wilson its old pressure ill take some more tomorrow

    pot.jpg
     
    Last edited by a moderator: Apr 7, 2019
  4. Keithedw Member

    Messages:
    34
    Location:
    Wirral
    This is the valve that gets clogged up with media ....it did it a couple off times today and what i noticed is that hose to the nozzle was getting block and no pressure coming out ...then it stops working because of the media ..
    could i blank off the 1/2" exhaust ?
    and is there a simpler way to sort this out ?
    cheers
     
    • valve2.jpg
    • valve.jpg
  5. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    I haven't seen this layout before, I'm guessing the valve is pneumatically operated and controls the air input to the pot. When the valve closes air from the pot is exhausted through the open port on the valve?

    You could try blanking the exhaust, this would have the effect of stopping the media flow gradually as pressure reduces in the pot.

    To my eyes the air input to the pot seems low, does it get covered by the media?

    You could try mounting the valve high up and using as wide a bore pipe from it as you can, thus any media feeding back will not reach the valve due to gravity.

    A non-return valve in the pipe between the valve and the tank will probably get blocked and it will stop air exhausting from the tank when the valve is closed.
     
  6. armalites Member

    Messages:
    4,651
    Herefordshire
    When you say the nozzle hose is getting blocked then either you have too much media for the air flow,not enough air flow for the media or the media could be damp or contaminated with oil.

    It's easy to assume more grit is better but it doesn't take much to take it over the edge.I would shut that medai valve and run the system for a while to check everything is clear, then open it 1/4-1/2 a turn at a time, there needs to be a balance of air/grit. That sort of unit needs a lot of air.

    Is this a cabinet that is new to you or is it something that has always worked fine but isn't now?

    The basic setup looks the same as my Vixen. You've got air coming in at the yellow lever feeding the input to the solenoid and the pedal via the red hose. The thin blue hose is the return from the pedal which operates the solenoid and allows the air out the other side.You could put a non return on the outlet of the air valve, I have a feeling my Vixen has one.

    The grit should never get anywhere near the valve because it will be under pressure until the pressue dies down but it is possible if the grit in the pot is higher than the air valve and when the pressure dies off it's trickllng back
     
  7. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    In theorey yes, but what happens is that when the valve exhausts the exhausting air carries grit with it.
     
  8. armalites Member

    Messages:
    4,651
    Herefordshire
    That means it has a 3 way valve when it should probably have a 2 way. There shouldn't be any need to vent the down stream air as the pressure will die very quickly anyway.

    That will explain why the nozzle is getting blocked, the air is dumping at the other end creating back flow and allowing the media to build in the hose.

    I was assuming the exaust was for the control valve as it needs to bleed air for it to work or the valve would stay open continuously but given it's 1/2 inch that's unlikely so block the port may well work.

    I've just had a look at mine and is doesn't not vent the downstream air, the air valve is simply off/on.

    I've just zoomed in on the picture and it is a diverter valve, I would be inclined to swap the inlet and outlet pipes so the flow is going in the correct direction(not sure that really matters) and put a blank in the open port. Putting a blank in the open port now will give the same result though and shouldn't cause any issues. The only worry is if the grit has already affected the valve.

    upload_2019-4-8_10-14-38.png
     
  9. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    ^^Blocking the exhaust port would convert that valve into a 2 way valve.

    Media can still block the nozzle as pressure dies, made worse if the bottom valve on the pot is open too wide.

    I fitted a valve on the top of my pot to release pressure quickly after turning the air supply off.
     
  10. armalites Member

    Messages:
    4,651
    Herefordshire
    I reckon blocking the port will cure the issue.

    Mine is a high end professional unit but it doesn't get a huge amount of use and I can still the odd issue with blockages. Once it's been running for a while and the grit has done a few cycles it all frees up nicely.

    I think it depends on what size of pressure pot you have, mine has quite a small pot built into the cabinet which vents very quickly. I have got one of those 20 gallon jobs that I used to use and that takes some time to bleed down and if you are not careful you end up over blasting or hiting a part you didn't want to :mad:
     
  11. Keithedw Member

    Messages:
    34
    Location:
    Wirral
    I've only had the cabinet a couple of weeks and the old valve was full of media so it must of been doing it to the previous owning ......I think it could be a mixture of what guys say .......I've plugged the exhaust of and changed the media for new ...seems to be working ok
    Think my compressor is not really up to the job I've been told it's about 25 cfm ...
    What size pipe work would you suggest to pipe it all in
     
  12. Keithedw Member

    Messages:
    34
    Location:
    Wirral
    I did
     
  13. Keithedw Member

    Messages:
    34
    Location:
    Wirral
    I did Have the valve filly open I've turned it right down aswell
     
  14. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    The way I set mine up was to turn all the valves off, open the supply valve to the pot fully, open the valve at the back fully, this should give a healthy blast of air through the nozzle. Give it 30 seconds to clear any crud out of the hose then slowly open the valve at the bottom of the pot until the stream of media out of the nozzle is barely visible.

    The air requirement depends on the size of the nozzle, mine wore out to about 3 to 4 mm dia and I had 2x 14 cfm compressors feeding the pot. Finer media will need more air.

    I had my regulator set to about 90 psi.
     
Advertisements