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vacuum pump inline air filter

D

Dennis DeVendra

Joined
Aug 23, 2009
Messages
21
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Location
Columbus, Ohio
Website
www.blindwoodturner.com
I just purchased a Gast vacuum pump. I am using the 1/8 inch barbs to hook up the air line. I want to put an inline air filter in the air tube. What is the best way to go? I purchased a commercial inline air filter yesterday. The filter is designed to be used with air tools. The problem is that the vacuum pulls the little plunger at the top instead of pushing it shut. I was thinking I could just remove the little plunger and just seal it with a piece of rubber or plastic. Does this sound right? What have others done?
 
On my air filter there is a plunger that allows the air to come in during vacuum. The filters in your reference sem to have the same feature. How do you close the hole?
Tony Pridmore said:
Dennis,

Surplus Center has air filters with 1/2" hose barb in and 1/4" NPT out. Price is $5.99. This is what I used on my Gast pump.


Tony
Click to expand...
 
That filter doesn't have a plunger. An open pipe runs through the housing. The internal filter screws onto one end and the intake barb screws onto the other end. If I recall correctly, threading on the barb fitting was not an NPT size. I didn't check myself, but vaguely recall reading that in someone's write-up about building a vacuum system for the lathe.

I suggest calling Surplus Center's technical support folks.

Tony
 
Dennis DeVendra said:
I just purchased a Gast vacuum pump. I am using the 1/8 inch barbs to hook up the air line. I want to put an inline air filter in the air tube. What is the best way to go? I purchased a commercial inline air filter yesterday. The filter is designed to be used with air tools. The problem is that the vacuum pulls the little plunger at the top instead of pushing it shut. I was thinking I could just remove the little plunger and just seal it with a piece of rubber or plastic. Does this sound right? What have others done?
Click to expand...

Don't forget that you need two filters. The large filter is inline with the line to the vacuum chuck to catch dust from turning and a small filter is needed on the open end of the needle valve that you use to control the amount of bleed for regulating the vacuum at the chuck. The amount of flow through the bleed valve is very small, so a small filter will do.
 
Bill Boehme said:
Don't forget that you need two filters. The large filter is inline with the line to the vacuum chuck to catch dust from turning and a small filter is needed on the open end of the needle valve that you use to control the amount of bleed for regulating the vacuum at the chuck. The amount of flow through the bleed valve is very small, so a small filter will do.
Click to expand...

Bill why is the second filter necessary.


Thanks,
Mike
 
Mike Stephens said:
Bill why is the second filter necessary.


Thanks,
Mike
Click to expand...

Because the vacuum pump is sucking bleed air into the line to reduce vacuum at the chuck and you want to insure that the air is clean, just as you want to insure that the air is clean coming from the chuck. Since the bleed valve is placed very closed to the lathe so that you can adjust it while turning, it will be located in dusty air (all air in your shop is dusty). Any kind of dust, but especially wood dust (which also contains silica) is going to be very abrasive to the moving vanes in the pump. Rebuilding the pump head is expensive so it makes sense to insure that nothing but clean air is passing through the it.
 
Here's an example of what Bill's talking about:

Vaccum Cart 6 500.jpg

The line from the vacuum chuck at the lathe enters the circuit at the lower right of the picture, into the big filter. (You'll recognize the filter as the same one Tony linked to.) The valve in the middle allows you to reduce the amount of suction that's applied to the chuck by bleeding additional air into the circuit. The smaller filter catches anything that makes it past the big filter, plus anything that enters through the bleeder valve. Another option would have been to put the small filter between the valve and the 4-way fitting. The pump is connected to the line that exits on the left of the smaller filter.
 
Vaughn said:
Here's an example of what Bill's talking about:

View attachment 3508

The line from the vacuum chuck at the lathe enters the circuit at the lower right of the picture, into the big filter. (You'll recognize the filter as the same one Tony linked to.) The valve in the middle allows you to reduce the amount of suction that's applied to the chuck by bleeding additional air into the circuit. The smaller filter catches anything that makes it past the big filter, plus anything that enters through the bleeder valve. Another option would have been to put the small filter between the valve and the 4-way fitting. The pump is connected to the line that exits on the left of the smaller filter.
Click to expand...


Why not just use the 1 big filter after the bleeder before the air goes into the pump?
 
Mike Stephens said:
Why not just use the 1 big filter after the bleeder before the air goes into the pump?
Click to expand...

I don't see why that wouldn't work. I don't know if the gauge is susceptible to problems from dust, but it would be pretty easy to reconfigure the circuit to put the gauge after the filter. In my case, I had ordered the bigger filter, then bought the rest of the parts as a kit from VeneerSupplies.com that included the smaller filter. Since i had both on hand, I used them.
 
Vaughn said:
Here's an example of what Bill's talking about:

View attachment 3508

The line from the vacuum chuck at the lathe enters the circuit at the lower right of the picture, into the big filter. (You'll recognize the filter as the same one Tony linked to.) The valve in the middle allows you to reduce the amount of suction that's applied to the chuck by bleeding additional air into the circuit. The smaller filter catches anything that makes it past the big filter, plus anything that enters through the bleeder valve. Another option would have been to put the small filter between the valve and the 4-way fitting. The pump is connected to the line that exits on the left of the smaller filter.
Click to expand...

There are a couple things that I would do differently. The first is to use a needle valve for the bleeder because it allows fine control of flow which is important because the vacuum level changes rather quickly with even just a tiny amount of flow. A ball valve is really for ON-OFF use and does not allow for fine tuning the vacuum level. I learned this one from the Tolly brothers (Jimmy and Johnny). Next, I would have the small filter located on the intake side of the bleed valve so that the intake is open to the atmosphere. Doing it this way keeps the bleed valve from getting cruddy with dust. Also, this protects the vacuum gauge from being a dust collector. The general idea is to protect as much of the plumbing as possible from allowing dust to accumulate. I would say that the big filter is in the right place because it is as close to the chuck as you can reasonably have it. When doing the plumbing, another consideration is being able to get a reasonably accurate vacuum reading. This means that the vacuum gauge should be close to the filter (on the protected side) and that the bleed valve should be located a bit closer to the vacuum pump than the gauge -- otherwise, the gauge would be indicating slightly greater vacuum than is actually at the chuck. A cross connector is probably OK, but I would be tempted to tee the bleed line off the vacuum pump side of the the cross. Finally, two additional valves are needed for the shut-down sequence -- I suggest using ball valves. One valve is used to open the intake port to atmospheric pressure without going through any plumbing. The other valve is used to block the intake port of the vacuum pump. Here is what Gast says that you need to do:
  1. Disconnect plumbing.
  2. Operate product for at least five minutes without plumbing.
  3. Run at maximum vacuum for 10-15 minutes.
  4. Repeat step 2.
  5. Disconnect power supply.
  6. Plug open ports to prevent dirt or other contaminants from entering product.
I follow this procedure, but I bet that most woodturners do not. I would think that one would want to take care of an expensive piece of equipment, but apparently not. Gast explains on their web site that the shut-down sequence is needed because the vacuum pump gets very hot during operation and if it not cooled down properly, a vane could crack or stick or the very hot aluminum pump body could cause a vane to jam.

Mike Stephens said:
Why not just use the 1 big filter after the bleeder before the air goes into the pump?
Click to expand...

See my answer above. We do not want dirty air anywhere in the plumbing except for the short length from the lathe to the filter.
 
Last edited:
Bill you bring up good points. That said, I've never felt the need to be able to fine-tune the vacuum with the bleeder valve. So far, I've only used mine either fully closed (about 21 inches of mercury) or wide open (about 15 inches). I don't think being able to dial it in at 18 inches would gain me a whole lot.

I hadn't seen or heard about the shutdown sequence you mentioned, particularly the extra valves. I just followed the plumbing ideas used by others on the VeneeringSupplies.com site, and used their recommended parts.
 
When a ball valve is fully open there is very little restriction on air flow. I suspect that because of the location of your vacuum gauge, the reading may not be an accurate indication of vacuum at the chuck. If the diameter of your vacuum chuck is small and if the turnings are thick walled, then it is true that the amount of vacuum is not critical. It does become more critical when a large diameter chuck is used and the turning is thin walled. It is also important to know if there is a lot of leakage through the wood. Some porous wood will let air pass through it like a sponge.

With respect to the cool down procedure, the usual response when I mention this to other woodturners in my club is that going through the cool down procedure takes too much time ... and since their vacuum pump has not broken yet, the cool down cycle is unnecessary. So the obvious meaning of the observation is that slow cumulative failures do not really exist -- only the sudden catastrophic ones are real. If a vacuum pump is just use briefly and you can hold your hand on it, then it is probably OK to skip the cool down procedure.

I found some new information in the Gast FAQ section yesterday that indicates that they have revised the necessary cool down to make it much shorter. I do not know if this is applicable to older pumps or just the new ones, but here is what they say:
Proper shutdown procedures must be followed to prevent pump damage. Failure to do so may result in premature pump failure. The Gast Manufacturing pumps are constructed of ferrous metals or aluminum which may be subjected to rust or corrosion when pumping condensable vapors such as water. Follow the steps below to assure correct storage or shutdown of the unit between uses:
  1. Never oil a non-lubricated unit.
  2. After using the unit, disconnect it from your application and allow the pump to run open for at least 3 minutes.
  3. Then block the inlet port and let the pump to pull a deep vacuum on itself for at least 5 minutes. (this lets the pump get very hot and will dry out any moisture that the pump has sucked into itself)
  4. Then after the 5 minutes open the intake and let the unit run for 3 minutes to cool down now the unit is ready for storage.
I think that the shorter cool down is much moe acceptable to users and some may even follow the procedure. 😀
 
You're right about the thin walls and big chucks. The first time I suck the bottom off a piece I'll probably be changing my tune about dialing in the amount of vacuum. 😱

And thanks for the info about the cool-down cycle. I can picture several ways I could add the necessary plumbing to essentially disconnect the pump from the circuit as well as block the inlet port.
 
Vaughn said:
You're right about the thin walls and big chucks. The first time I suck the bottom off a piece I'll probably be changing my tune about dialing in the amount of vacuum. 😱

And thanks for the info about the cool-down cycle. I can picture several ways I could add the necessary plumbing to essentially disconnect the pump from the circuit as well as block the inlet port.
Click to expand...

I installed a brass tee right on top of the inlet port and installed two ball valves. One opens to the atmosphere and the other is inline with the plumbing to the vacuum chuck. When doing the "open" part of the cool down, I simply open both valves, but most of the flow is through the one that goes straight to the outside. For the closed part of the cool down, close both valves. Before I store it, I make sure that both valves are closed.

I have not imploded one yet, but I have applied too much vacuum that led to a permanent dent in the wall of a bowl. Also for mesquite which I turn green, too much vacuum can suck the "stuff" out of the wood and leave it much more porous than before. This really surprised me when I first saw it. Tape can help a bit as well as reducing the vacuum.
 
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