What about a normal air fitting? Put the female end on the jar and the male end on the pump. They hold pressure file, but I don't know if their seals hold vacuum?
What about a normal air fitting? Put the female end on the jar and the male end on the pump. They hold pressure file, but I don't know if their seals hold vacuum?
In reply to WonkoTheSane (FS) :
It should work, but I think it would be overkill for this application.
For the lid of the jar a thick piece of smooth plastic or metal would work, seal it up with a little oil of your choice on the lid. You may have to wet sand it a bit on a flat surface (table saw table or piece of glass) to get a flat and smooth enough surface. I would do any actual vacuuming inside a 5 gallon pail with a lid though just as a safety precaution for the inevitable reverse boom. Mason jars are not 100% ideal.
Although for $120 you can buy what you actually need...
white_fly said:In reply to Curtis73 (Forum Supporter) :
I looked for Schrader valve to npt adapters and didn't find anything, but I'm going to keep looking. Schrader valves are so cheap that it seems like a great choice.
HD has 1/4" NPT schrader valves. Plumbers use them to test iron pipe for leaks. Auto Parts stores have threaded schraders to replace on wheels.
1/4" NPT schrader valve. This is sold in the air compressor aisle and also the plumbing repair aisle at HD. It is used as a means to fill an air tank, or for testing plumbing.
Bolt-on schrader valve. These are simply replacement tire valves that bolt on instead of pop in the wheels
A trick I have used for bleeding brakes is to cut a plate of 1/8" steel and glue some high-durometer rubber on one side. Drill a hole in the center and tap it for 1/4" NPT. Then screw in a male air fitting.
I can use it for vacuum (although the industrial air fittings sometimes leak under vacuum) or pressure.
Using pressure, clamp it on top of a brake master cylinder and give it 10 psi. Great way to bleed brakes with one person.
In reply to Curtis73 (Forum Supporter) :
You're completely correct. I should've been more specific that I was looking for a fitting that would screw onto the threaded portion of the schrader valve. I was thinking if I could reverse the insert in the schrader valve, I could essentially have a check valve that would seal in the vacuum.
But maybe I'm overthinking this. Maybe the simplest answer is an upside down schrader valve attached to a regular mason jar lid. Insert the entire jar into a vacuum chamber, suck all the air out, release the vacuum in the chamber, and then simply remove the jar which will still have vacuum inside it. I can have a vessel that should maintain vacuum for an extended period of time for $3 or $4 all in.
The only question I'm left with would be how much vacuum would I give up due to the springing action of the valve insert?
I gotcha. Scupper-like.
Could you remove/cut the spring? I don't think the spring would amount to much pressure itself. It's mostly there to provide a positive direction and help the valve seat while not in a position that gravity does the work.
If you install it upside-down, gravity should return the valve to the proper position. Then air pressure is doing the work. I don't think the spring itself matters a hill of beans to the actual sealing properties of the valve. I think it is just there to positively engage the seal so that air pressure can do the actual work. If you have gravity doing that work for you, I don't think the spring is necessary.
I think the secondary tank is a viable idea, but I don't think it's necessary. If your lid had one of those NPT Schraders with the NPT on the outside, you then have a 1/4" NPT male thread to play with and adapt to anything you want for the pump.
Like this: Destroy the spring in the valve's core and let gravity do the work. Then you have NPT on top which can be adapted to anything. Maybe a little epoxy around the lid where the NPT fits for integrity/sealing.
In reply to Curtis73 (Forum Supporter) :
That's exactly like what I want to do. Maybe npt to a nipple or press to fit connection, maybe just venting to a vacuum chamber; but the upside down schrader is at the heart of it.
Unfortunately, the breakopen pressure is quite high on most schraders. This is usually not a concern because in normal operation the valve is depressed while it is being filled. In my case, that's not possible. I think I'll stop by a parts store and see if I can remove a spring without affecting the seal. I have found that springless valves exist, but they are specialty items and I'll have to make some phone calls on Monday to go down that road.
Oh.... just had an idea.
pneumatic check valve. You're looking for the lowest cracking pressure. This one is 0.28 psi, which is pretty darn low. Probably lower than the vacuum pump can get to.
If you think about it, 28mmHg of vacuum is 0.95 bar, or a delta of -13.7 psi. So even a 28mmHg pump will only take you down to an absolute pressure of about 1 psi. As long as the cracking pressure of the valve is less than the vacuum available from the pump, it won't be the limiting factor. This particular valve is also rated for 230 psi... far above the 14.5 psi that opposes an absolute vacuum, which it will ever see.
In reply to Curtis73 (Forum Supporter) :
The check valve may very well be the right solution. The trouble is that it's $15. $15 for a check valve, plus more money for a bulkhead fitting and a way to connect the check valve to a hose could easily be $30. For a single jar, it's no big deal. For 10 jars, the schrader valve is much more attractive. $300 buys a lot of pretty wood.
Curtis73 (Forum Supporter) said:A trick I have used for bleeding brakes is to cut a plate of 1/8" steel and glue some high-durometer rubber on one side. Drill a hole in the center and tap it for 1/4" NPT. Then screw in a male air fitting.
I can use it for vacuum (although the industrial air fittings sometimes leak under vacuum) or pressure.
Using pressure, clamp it on top of a brake master cylinder and give it 10 psi. Great way to bleed brakes with one person.
I have a small collection of extra master cylinder caps with a 7/16" (might be 27/64ths, might be 29/64ths) hole drilled in the top and a rubber tire valve snapped in.
Then I use a bike air pump to push the fluid through.
When your clutch master cylinder fails when you're getting ready to go to the dragstrip, and you remember something a friend said about using gear oil in the clutch hydraulics to limp a bypassing master along, it is the ONLY way to bleed the clutch. Air bubbles hang in 80W90 forever. But I made it to the strip. The clutch hydraulics went another three or four years before starting to bypass again.
But don't try it if you drive the vehicle in the winter. Push the clutch down, pedal stays down for a good 4-5 seconds.
True. I happened to link to McMaster which is often the highest possible price.
Pete. (l33t FS) said:But don't try it if you drive the vehicle in the winter. Push the clutch down, pedal stays down for a good 4-5 seconds.
It's a special auto-engaging clutch. Just take your foot off the pedal and apply a little gas 
So, the springless valve cores are available. For a price, obviously. $0.18/each as long as I get at least 2,000 of them.
Anyone in the market for 1,990 springless valve cores?
What is the market for springless valve cores? Who uses them? For instance, if it's a trucking thing, can you hit up a truck tire place and give someone $5 for a handful of cores?
I also thought of a cheaper check valve setup by using automotive vacuum check valves. Not exactly what you seem to be going for, but these are $1.50 each, they have a cracking pressure of 0.07 psi and a backpressure rating of 45 psi which is about 3 atm.
I can't figure out who uses them. They're sold as part of "tank valves" by Schrader Pacific. If I knew who is ordering 2,000 at a time, I'm sure I could pick up a few.
Those check valves look like a good option. I wonder how well they would hold vacuum over, say, 48 hours. And they may not be designed to fit bulkheads, but they're a little bit of silicone away from an easy seal.
Another option for me to try in the short term is presta valves. They're springless and probably free at the local bike shop.
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