Harbor Freight sand blasting cabinet questions

[NikolaiBorjeski]

Recently got a harbour freight / princess auto sand blasting cabinet on sale. I did the most recommended mods to it before using it, namely sealing the cabinet with silicone and replacing the pickup tube with the bottom mounted metering valve.

The cabinet has a water separator plumbed in, and all of the lines feeding it are 1/2", line pressure is 100psi.

My issue is that it doesn't siphon sand properly, regardless of what I have the metering valve set to. It will blast sand for about a half a second after pulling the trigger, but stops almost immediately. What am I doing wrong?

 

[Inferno]

Recently got a harbour freight / princess auto sand blasting cabinet on sale. I did the most recommended mods to it before using it, namely sealing the cabinet with silicone and replacing the pickup tube with the bottom mounted metering valve.

The cabinet has a water separator plumbed in, and all of the lines feeding it are 1/2", line pressure is 100psi.

My issue is that it doesn't siphon sand properly, regardless of what I have the metering valve set to. It will blast sand for about a half a second after pulling the trigger, but stops almost immediately. What am I doing wrong

Here's how to fix it, and why it will work.

First, you can get rid of the regulator. It's not needed. You can keep it if you want but I wouldn't.
Remove all your media from the unit. It will be in the way for the next step.
Measure the opening at the bottom of the hopper. I'll pretend it's 4 inches.
Add a baffle that's about 2", halfway blocking the media from getting to the input. What you need is just enough getting to the input with a pocket of air. A mound of media works well as it will be drawn into the tube WITH air. All media will clog it too much.
The reason it works is that the media is crystals, unless it's new glass bead, and those will interlock pretty fast and clog the hose.

Adding in the regulator, the way you have it, just gives it a smaller orifice to plug up.
If you insist on having the regulator move the flow vertically for best results.

Making this small baffle change on my old media blaster took it from a piece of crap I almost recycled to a tool I used every day for an entire summer.

Don't forget to get more tear off material. They fog up fast and if you run without one you will have fogged glass forever.
Also, adding a light inside helps. I used a fluorescent 18" shop light in mine.
Add a catch filter on the vent hole. It makes a huge difference in the mess.

 

[NikolaiBorjeski]

Here's how to fix it, and why it will work.

First, you can get rid of the regulator. It's not needed. You can keep it if you want but I wouldn't.
Remove all your media from the unit. It will be in the way for the next step.
Measure the opening at the bottom of the hopper. I'll pretend it's 4 inches.
Add a baffle that's about 2", halfway blocking the media from getting to the input. What you need is just enough getting to the input with a pocket of air. A mound of media works well as it will be drawn into the tube WITH air. All media will clog it too much.
The reason it works is that the media is crystals, unless it's new glass bead, and those will interlock pretty fast and clog the hose.

Adding in the regulator, the way you have it, just gives it a smaller orifice to plug up.
If you insist on having the regulator move the flow vertically for best results.

Making this small baffle change on my old media blaster took it from a piece of crap I almost recycled to a tool I used every day for an entire summer.

Don't forget to get more tear off material. They fog up fast and if you run without one you will have fogged glass forever.
Also, adding a light inside helps. I used a fluorescent 18" shop light in mine.
Add a catch filter on the vent hole. It makes a huge difference in the mess.

I appreciate the response, though I'm not entirely sure what you're proposing. By regulator do you mean the entire metering valve? Or just the ball valve connected to it? I'm having a hard time picturing what the baffle should look like and where it gets the air from.

I cloned this design, it seems to be proven and confirmed working, I just don't understand why my setup doesn't. I will try resealing the pipe fittings and running it with less media, currently there's probably 4-5 gallons in it, maybe that's too much.

 

[pontiac428]

I have hemmed and hawed over adding a media pickup to mine. What I ended up doing after wearing abrasive holes in the original pickup tube is I installed a new pickup tube made of thicker walled stainless that is a few inches longer than the original, and totally straight instead of curved at the end. This put the pickup of the tube a good 6" deeper into the hopper. I made that mod in 2006 IIRC, and it's been solid ever since.

One other change I have made to my blasting program is reducing the pressure in the blast line to 40-60 psi, which is 3-4 bar for the rest of the world. Reducing pressure made no difference in blasting performance, but it did improve media feeding and media distribution. Turns out, there's such a thing as too much air pressure in these sand/air emulsifiers. I thought the manufacturers were just a bunch of pink undies wearing ninnies for publishing low operating pressure specs in the cabinets, but it turns out there's science behind it!

 

[Inferno]

I appreciate the response, though I'm not entirely sure what you're proposing. By regulator do you mean the entire metering valve? Or just the ball valve connected to it? I'm having a hard time picturing what the baffle should look like and where it gets the air from.

I cloned this design, it seems to be proven and confirmed working, I just don't understand why my setup doesn't. I will try resealing the pipe fittings and running it with less media, currently there's probably 4-5 gallons in it, maybe that's too much.

OK, I missed something when I looked at your pictures. I see where thy are going with this.

Did you add the baffle

Are you getting too much sand or too much air when you say it stops working?
The concept is still the same as what I said. If there's a clog, before the air inlet, you won't get sand.

The trick is to keep the media "fluffed" at the inlet tube.
Also, as said above, too much air will backflow into the pick up tube. You need just a tiny bit less air flow than the nozzle will allow.

 

[NikolaiBorjeski]

OK, I missed something when I looked at your pictures. I see where thy are going with this.

Did you add the baffle

Are you getting too much sand or too much air when you say it stops working?
The concept is still the same as what I said. If there's a clog, before the air inlet, you won't get sand.

The trick is to keep the media "fluffed" at the inlet tube.
Also, as said above, too much air will backflow into the pick up tube. You need just a tiny bit less air flow than the nozzle will allow.

Seems like too much air, the sand just stops flowing. If I look in the clear tube going to the gun while the trigger is pulled I can see the sand "jump" up and down, but it doesn't make it. Almost like it's not creating enough suction.

I've tried sealing the pipe fittings with tape as they weren't before, and running the line pressure lower as well as reducing the amount of sand in the cabinet, none of this seems to have made a difference.

Here's a picture of the inside of my pickup. I cleaned the pipe dope out after noticing it in these photos.

 

[pontiac428]

The venturi in the blast nozzle works on the Bernoulli principle. That means a zone of low pressure is induced in the tube, which should draw "emulsified" sand into the nozzle. The bleed valve is how you control the aeration of the emulsion, and only works because the "mixing chamber" is long and horizontal. If you don't allow enough air in, the emulsion will be too dense to flow. I would start with the valve open and close it slowly while holding the trigger, and stop at the point where it really sings. It should be a set it and forget it type of thing. If you change media, say from silicon carbide to glass beads, you will need to re-calibrate the bleed.

Speaking of media, I would like to put out a public safety announcement- almost all of the slag-based media for blasting being sold is contaminated with beryllium. With copper slag, beryllium is an expected contaminant. With coal slag, anything goes, but mercury is top ugly there. Much of the slag media is being imported from china, sold to non-commercial entities (that means you and me when we go to Harbor Freight or Home Depot), and is not being monitored by the gubmint. The Navy was enticed into using a ton of the stuff (surely a business deal negotiated on the golf course) that came from domestic copper production (i.e. Anaconda mine) and it was heavily contaminated with toxic, nasty, life-shortening beryllium. The company was so peeved when the Navy sent the material back that they sent reps to come watch how we determined that beryllium was there. They left quietly, slipped out the back door. They sell this stuff cheap with names like "black magic" or "black beauty". Do not be fooled, they are selling industrial waste to you as a "product" now. Please, all Hobby Machinists, stick with glass beads, aluminum oxide, and silicon carbide. When your media is worn out, bag it and throw it away, don't keep toxic metal powder in your hopper for later inhalation by just "topping off" with fresh media. And if you can, rig up a vacuum recovery system to keep the dust down. That old paint we are removing might be full of lead, chromium, even arsenic if it's marine paint. Bad stuff to inhale!

 

[Inferno]

Seems like too much air, the sand just stops flowing. If I look in the clear tube going to the gun while the trigger is pulled I can see the sand "jump" up and down, but it doesn't make it. Almost like it's not creating enough suction.

I've tried sealing the pipe fittings with tape as they weren't before, and running the line pressure lower as well as reducing the amount of sand in the cabinet, none of this seems to have made a difference.

Here's a picture of the inside of my pickup. I cleaned the pipe dope out after noticing it in these photos.

Just an opinion but I think the pipe is too big.

 

[Boswell]

Probably not the solution to your problem but when I was having problems with my sand not picking up after a few minutes of blasting. I found that If I kicked the lower section it would work again for a few minutes. I added a vibrator to the lower section and now the cabinet works just fine.

 

[Inferno]

Probably not the solution to your problem but when I was having problems with my sand not picking up after a few minutes of blasting. I found that If I kicked the lower section it would work again for a few minutes. I added a vibrator to the lower section and now the cabinet works just fine.

Is that why she's been so mad?