I’m not sure how much sand is supposed to come out of the nozzle. I have a Clemco pot with a regular flat sand valve, and I’m not sure where to set the handle for the best performance.
The abrasive stream coming out of the nozzle will be surprisingly lean! When you have the abrasive valve set right, you will hardly be able to see abrasive coming out of the nozzle at all, and this high-velocity, thin mixture of air and grit will deliver the best performance possible.
On the other hand, send too much abrasive through your hose and nozzle, and you will notice very poor performance. This is because too much abrasive slows down the air as it travels through the hose and nozzle. It’s important to keep the velocity up because the faster the abrasive particles fly, the better they impact the surface and do their job stripping away old coatings or rust, and preparing the surface for the next coating.
The Clemco Flat Sand Valve is a classic, straightforward metering valve. Setting it to the right volume is simple, but it’s easiest to do with two people. Be sure to wear all appropriate safety gear and follow this procedure:
- Close the abrasive metering valve by rotating the lever-shaped handle all the way to either side. This is the “Off” position, while putting the handle straight in the center is completely open. The “full open” position is rarely used for blasting. More on that later.
- Next, have the blast operator squeeze the remote control handle to begin blasting. Since the abrasive valve is all the way closed, only air will come out of the nozzle (after any grit in the hose has been flushed out).
- Listen to the sound the nozzle makes. Typically, a good-condition Venturi nozzle makes a high-pitched whistle sound when just straight air is passing through it. To me, it sounds like a jet engine. If it’s not whistling, perhaps you should make sure the nozzle isn’t worn out and ready for replacement.
- Once the nozzle makes that high-pitched whistle, begin rotating the handle slowly. As grit is introduced into the air stream, the sound coming from the nozzle will change. When the whistle sound goes away, you’re getting close. Have the operator aim the blast stream onto your work surface so you can adjust the valve to achieve the maximum performance. He can give you a thumbs up if your adjustments are making his job easier, or a thumbs down if the blast stream isn’t as good as it was before.
- Once you have it dialed in, just leave the handle there. You’re all set!
If the abrasive is spraying out of the nozzle very generously, like water out of a garden hose, you will find that it’s not impacting the surface very hard. Turn down the abrasive.
If the nozzle is sputtering and abrasive is flowing out in heavy spurts, the valve is definitely open more than necessary. However, there are times when opening the valve all the way is necessary. For example, it’s easiest to empty all of the abrasive from your blast machine with the abrasive valve all the way open and the nozzle removed from the hose.
You can open the flat sand valve all the way if you believe there is a clog of moist abrasive in the bottom of your pot.
What if this doesn’t work for me? The Flat Sand Valve handle passes to both sides because that allows the user to get longer life out of the metering plate inside of the valve. Once the metering plate wears on one side, turn the handle the other direction and you can use a fresh portion of this metering plate. If you can’t get your abrasive metering valve to work, no matter where the handle is turned, the metering plate could be ready for replacement. And with Clemtex, parts are always just a click or phone call away.