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How to set Schmidt Micro abrasive metering valve for optimum blasting

BlastOne’s Master Technician, Kerry Cooper, discusses how to set the Schmidt Micro abrasive metering valve for optimum blasting


So, this blue knob here is the end of the valve. The valve is called a microvalve. So, this system as I said before is micro combo. That’s a combo valve with the top micro out down the bottom.

The microvalve, what it does is by adjusting that valve is it enables the flow of grit to enter into this pusher line – air line arrangement and into your blast hose.

So, how do I know how much grit is coming out of there? Whether it’s the right amount or not, you’ve got to remember that you can actually flood the blast hose with grit if you open that valve too much.

So, therefore, you impede the blast, you’re wasting grit and you’re not achieving the profile that you’re looking for. So, unless is more in this case.

So, what I normally do is with that valve I wind it in until it stops so I can one into all the way until it stops. So, that means that the piston in that valve hits the seat and then what I’ll do is I wind it back 3 ½ to 4 turns. That gives me an indication of somewhere where I need to be in the realms of how much grit flows through.

So, how do I check then if I’ve got the right amount of grit? How do I know? You’ll notice that when you screw that valve all the way in, push the safety pin in, and depress the deadman handle, there’s a screaming noise. The screaming is always indicative the fact is only air coming through here.

So, the scream originates from where the venturi of the nozzle starts and the screams that exit is just basically the amount of air coming out. So, once you start introducing grit into that airflow, the scream diminishes.

So, you’ll notice that with the valve wound all the way in and you open the deadman, it’ll scream. However, you let release the deadman and wind this counterclockwise, 3 ½ to 4 turns, depress the pin, I open the deadman, the grit will start to slowly come out at the end of the nozzle. I say slowly. You’ve got to remember that in this flow, there’s the length of hose which is normally 15 meters or 50 foot so that grid has to join the air stream and end up all the way out here.

So, basically, it’s a slow wait and once it does have grit then there is grit lying in the line. So, each time you depress the deadman, the grit isn’t too far behind it. But in that first initial flow of grit, it’s a little bit slower than normal. So, be patient. Just wait for the grit to come out.

Now, when the grit comes out, you’ll notice that when you depress the safety pin and open the deadman with all your appropriate safety gear on. Whilst you’re blasting, you’ll see that the media starts to exit from the end of the nozzle and starts cutting whatever it is you’re looking to remove from the substrate.

So, if I’m concerned, I’ve got too much grit, what you’ll find is when you release the deadman and inspect the grit, you’ll find that it’s not what we call spent. So, when you when grit is spent that means that’s been smashed and shattered, usually utilizing the velocity of which it exhausts the glass nozzle.

But if it got too much grit and you find that that spent grit looks like brand-new, I think this help. I’ll hang on a minute. I’ve got too much grit.

So, how do I facilitate the appropriate metering of that valve? To be quite honest with, the easiest way to do it is if I’ve rounded out 3 ½ to 4 turns, bring the nozzle back to the blast pot, open, depress the safety pin, depress the deadman handle and watch the grit hold it up to the light and watch the grit exiting with the air stream.

Ultimately, what you’ll find is that you’ll have like a mantle shape come from the end of the blast nozzle and if you hold it to the light appropriately, you’ll see that it’s slightly blue and its kind of blue tinge to it, blue color that is absolutely spot-on the amount of grit you need.

So, what happens is above too much grit that mantle diminishes with the amount of abrasive that he exits the nozzle and if I have less grit or not enough grit, you’ll find that there is no mantle, and the nozzle just screams.

So, in between those two parameters of no mantle and scream, there is a little blue shape that is quite easily defined in the appropriate light to see that that’s there. So, just off scream and just under flooding is the right amount of grit to make that meet easier for you.

Again, to understand is that if I open that valve too far, you’ll find that the noise of the nozzle is softened. So, it becomes dull and deadened. That again is an indication you’ve got too much grit. Also, you’ll find that it tends to flood the surface.

One thing to remember, if you open that valve too far and you stop the operation by releasing the deadman when the valves open too far.

Remember what I said there’s only pressure in the top of the pot. This grit down here from the conical section falls of its own volition. So, if you open that valve too far, you’ll have a flooding of abrasive in the bottom of this valve that tends to block the pusher line itself when you open that.

When you depress the safety pin and open that deadman, again, you’ll find that the hose is starting to push towards you, push away from you. It has an inertia type when it pushes away. It also comes back at the same speed. That means that you’ve filled the hose or the blast hose with abrasive to such an extent that it’s stopping the air flow.

So, the air has to eventually clear that grit, the consequence of that will be all of that grit will accumulate towards the end of this nozzle and remember what I said, it’s a venturi nozzle. So, it’s large to small.

So, as the grit is trying to exit and the air still pushing it out, you’ll find that you’ll have an inertia or reaction with the nozzle itself pushing back on you. So, it pays never to open that valve all the way up.

Primarily, if you’re opening that valve, there’s something wrong somewhere in the system. You must have excessive moisture. Nine times out of ten, you’ll find that. It’s because there is no aftercall or air prep in the line to remove excessive moisture.

So, moisture contributes to the amount. You have to open this valve to appropriate the amount of grit to flow through there. Moisture tends to coagulate the abrasive and stops its free flow back into that valve.

So, all we’re looking for here is free flow of grit or abrasive into this valve. Don’t open the valve too far and you’ll always have the appropriate facilitation of grit in relation to the amount of air you have coming out at the end of the nozzle.

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