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What to do with this air pump?

Old 06-23-21, 12:30 PM
  #1  
Altair 4
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What to do with this air pump?

So I have Serfas tcpg tire pump which I very much like. The head works on both Presta and Schrader stems without having to change anything.

The other week, I was helping my neighbor's Girl Scout troop get ready for a group ride. After inflating a couple of really low tires, the resistance in the handle was increasing and each down stroke was making a squeaking / squealing noise. It's as the cylinder heated up that it got harder and harder to use. It got to the point where I gave up on it and starting using a Ryobi battery-powered pump.

Simple tool, right? What can go wrong? Before I start taking it a part, I was wondering if anyone had any suggestions on a fix? Does it need oil or lubricant on the end of the piston? THe thing is making me feel stupid.

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Old 06-23-21, 12:35 PM
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Is it working now, that it has cooled off?

Boyles law specifies that compressing a gas will cause it to heat up. It could be that you did this so many times you just exceeded the design limits of that little pump at the time.
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Old 06-23-21, 03:02 PM
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Yes, it works okay after it cools down - but it starts the noise and resistance after, say, bringing two 700 x 35's up by 20 PSI. This wasn't an issue when the pump was new - you could pump up tires from zero PSI without this happening. I sorta thinking about opening it up and see what's what inside.
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Old 06-23-21, 03:24 PM
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There may be a replaceable piston head or ring. At the very least, try a little grease on it.
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Old 06-23-21, 03:34 PM
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Originally Posted by Altair 4 View Post
Yes, it works okay after it cools down - but it starts the noise and resistance after, say, bringing two 700 x 35's up by 20 PSI. This wasn't an issue when the pump was new - you could pump up tires from zero PSI without this happening. I sorta thinking about opening it up and see what's what inside.
I know one pump I have allows the whole push rod and assembly to come off the tube by just unscrewing the top at the tube. I did that a few times accidentally. Never had to grease it though. But yeah, best idea is just to look/see what there is and how you might lubricate it.
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Old 06-23-21, 05:47 PM
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I've taken pumps apart before to grease the little flap that seals around the piston. You could give it a try if its not too difficult to take apart.
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Old 06-23-21, 06:00 PM
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I've used silcone lube on mine before I got the Ryobi pump.
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Old 06-23-21, 06:27 PM
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Last time I took apart my 1970s frame pump to fix it I found it used leather for the piston seal. To my surprise leather is still used today and I was able to get a replacement.
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Old 06-23-21, 07:06 PM
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Originally Posted by noisebeam View Post
Last time I took apart my 1970s frame pump to fix it I found it used leather for the piston seal. To my surprise leather is still used today and I was able to get a replacement.
Last floor pump I took apart was years ago, but it was leather and I was surprised.
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Old 06-23-21, 07:25 PM
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Old 06-23-21, 07:26 PM
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if it's unreliable compared to when it used to be, I'd chuck it.
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Old 06-23-21, 08:00 PM
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This marketing bit explains why leather: https://blog.silca.cc/uniquely-silca-the-leather-washer

It may give insight into why Altair's pump is heating and binding - some lube should help no matter what the washer material. Alternately you could build a water cooling system for it.

Hmmm, so there are such a thing as vegan floor pumps...
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Old 06-23-21, 08:07 PM
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Originally Posted by Altair 4 View Post
So I have Serfas tcpg tire pump which I very much like. The head works on both Presta and Schrader stems without having to change anything.

The other week, I was helping my neighbor's Girl Scout troop get ready for a group ride. After inflating a couple of really low tires, the resistance in the handle was increasing and each down stroke was making a squeaking / squealing noise. It's as the cylinder heated up that it got harder and harder to use. It got to the point where I gave up on it and starting using a Ryobi battery-powered pump.

Simple tool, right? What can go wrong? Before I start taking it a part, I was wondering if anyone had any suggestions on a fix? Does it need oil or lubricant on the end of the piston? THe thing is making me feel stupid.

Altair 4
I suspect that your check valve has failed. The check valve is buried in the foot peg and may not be serviceable. Best to contact Serfas.
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Old 06-23-21, 08:50 PM
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My $8 Harbor Freight floor pump did that after six years. Rubber seal. I put some silicone spray in there. If it eats the rubber, I get a new pump,
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Old 06-24-21, 05:11 AM
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Air has particles in it that accumulate. I have taken apart pumps and cleaned them. I have also replaced a rubber o-ring in a frame-type pump with a stock part from the hardware store.
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Old 06-24-21, 07:06 AM
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Originally Posted by Arthur Peabody View Post
Air has particles in it that accumulate. I have taken apart pumps and cleaned them. I have also replaced a rubber o-ring in a frame-type pump with a stock part from the hardware store.
No. While air can have particulates, they are on the order of 10g/cubic meter or 1/100,000th of a gram/ cubic meter. Assuming about 150mL per tire at 100psi, that about a liter of air at atmosphic pressure or about 0.01g/tire. To get a gram of particulates into the pump, ten million tires would have to be pressurized.

A seal fail on the plunger also wouldnt result in the problem Altair 4* describes. Plunger seal failures would result in no resistance at the handle during pumping because the air column being compressed would leak past the seal. The squeal he describes is probably air being forced past the seal as the pressure increases in the tube due to the failed (or failing) check valve but the seal isnt the problem.


*Now I get it. Do you want to be Captain Adams, Morbius, or Robby?
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Old 06-24-21, 09:14 AM
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Originally Posted by cyccommute View Post
*Now I get it. Do you want to be Captain Adams, Morbius, or Robby?
Oh, it works on more levels than that. Star Trek, Stephen King's "The Tommyknockers," and others. Actually, I'm into backyard astronomy, so it covers all my bases.

If I get a few minutes over the weekend, I'm going to try and take the pump apart and see what's going on in there.
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Old 06-24-21, 09:19 AM
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If a couple drops of oil down into the cylinder doesn't fix things, replace the pump.

Note: wax is not recommended for this application.
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Old 06-24-21, 10:08 AM
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all else fails & you're determined to keep trying to save the pump, pour in some tubeless tire sealant above the plunger area if you have it around. It may or may not be effective & could cause some snot at the feeding valve. I've used Slime* in a cheap 12v car pump by backfilling it & it worked. Sold the vehicle with it in stored in the trunk.
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Old 06-24-21, 10:15 AM
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Originally Posted by Altair 4 View Post
Oh, it works on more levels than that. Star Trek, Stephen King's "The Tommyknockers," and others. Actually, I'm into backyard astronomy, so it covers all my bases.

If I get a few minutes over the weekend, I'm going to try and take the pump apart and see what's going on in there.
Star Trek used Altair 6. But Forbidden Planet used started it all. I recently finished the novelization of the movie by W.J. Stuart. Waiting for my wife to read it so that we can watch the movie again. One of my favorite 50s sci-fi movies and it does still hold up.
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Old 06-24-21, 10:43 AM
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Originally Posted by cyccommute View Post
A seal fail on the plunger also wouldnt result in the problem Altair 4* describes. Plunger seal failures would result in no resistance at the handle during pumping because the air column being compressed would leak past the seal. The squeal he describes is probably air being forced past the seal as the pressure increases in the tube due to the failed (or failing) check valve but the seal isnt the problem.
Exactly, IMO.
The increasng pressure/resistance at the pump handle is a sign of 'air with nowhere to go' - so check valve or a problem at the head at the end of the hose, or a Presta valve not loosened, or ???
If it's a simple thing to do, removing the head at the end of the hose, or removing the hose from the pump will help to localize the problem.

Squeaking during pumping by itself and/or decreasing resistance at the pump handle would be (IMO) signs that lubrication of the piston seal was required.
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Old 06-24-21, 11:20 AM
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Originally Posted by cyccommute View Post
I suspect that your check valve has failed. The check valve is buried in the foot peg and may not be serviceable. Best to contact Serfas.
I agree, the check valve is the most likely culprit. It's one of the only moving parts, and it will constrict air flow if it doesn't open fully.

The Serfas TCPG is a pretty cheap pump, so I expect the components are of mediocre quality. I just checked the Serfas replacement parts page, and they don't offer a check valve.
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Old 06-24-21, 12:26 PM
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Originally Posted by terrymorse View Post
The Serfas TCPG is a pretty cheap pump, so I expect the components are of mediocre quality.
It may have been cheap, but I got 10 years out of it. I really can't complain. Not being one to simply replace something, I thought I'd give it a try to fix. No complaints if it's dead - I got my money's worth out of it.
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Old 06-24-21, 06:05 PM
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Originally Posted by cyccommute View Post
I suspect that your check valve has failed. .
Potential conflicting evidence to that model:
Originally Posted by Altair 4 View Post
Yes, it works okay after it cools down - but it starts the noise and resistance after, say, bringing two 700 x 35's up by 20 PSI.
Of course it is possible check valve fails as it warms.

Originally Posted by cyccommute View Post
Plunger seal failures would result in no resistance at the handle during pumping because the air column being compressed would leak past the seal.
Or the seal increases resistance as it warms due to lack of lube.

Last edited by noisebeam; 06-24-21 at 06:08 PM.
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Old 06-24-21, 06:19 PM
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Originally Posted by noisebeam View Post
Potential conflicting evidence to that model:


Of course it is possible check valve fails as it warms.


Or the seal increases resistance as it warms due to lack of lube.
Ive had this kind of failure with a Lezyne Steel Drive. The pump started resisting pushing down and little to no air was going into the tire. I contacted Lezyne and was informed that the Steel Drive has a plastic check valve that isnt meant for heavy or extended usenot that my using it at home was what I would call heavy or extended use. They suggested the Lezyne CNC pump which is rebuildable and has a more robust check valve. I suspect that part of the check valve is made of polyethylene which has a low melt point. Over a lot of tires, there is a lot of heat generated and the check valve may melt into place or deform.

Seals wouldnt really cause an increase in resistance. Worn seals just let air blow by when pressure is appliedthink old leather pumps
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