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Next project - Interesting or daft?

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Next project - Interesting or daft?

Old 06-03-20, 03:28 PM
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mikeread
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Next project - Interesting or daft?

moderator note: I merged the copies of this thread with comments, so if they seem a little jumbled, that's why -- unterhausen

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Old 06-03-20, 03:29 PM
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Next project - Interesting or daft?

I have been experimenting with stowing pumps down the seat tube for some time.

Now I suspect this idea will get ridiculed by some as there are already plenty of perfectly good solutions to stowing a pump. However I like to try something new and this idea does have some plus points:

Advantages
1 The pump is hidden away and does not mess up the look of your bike.
2 It is secure and will not fall off your bike or out of your pocket. You will not forget to take it with you either.
3 Because of the space available you can, (in theory) have a very long pump, old style frame pump length which will pump much quicker than a mini pump.

Disadvantages
1 Having to explain why your pump is in your seat tube when you get a puncture - and probably getting laughed at.
2 Having to remove the seat post to get at the pump.

I have had a relatively long mini pump stored in my seat tube for a year now and have had it out in anger twice. It takes a few seconds to get at the pump, but because of its length, it requires 150 pumps to get to 85 psi instead of 250, which my alternative (decent) mini pump takes. This more than compensates for the effort to remove the pump from the seat tube.

Now I know the concept works I am planning to build a pump to maximise the space in my seat tube. I have about 500mm to play with and should be able to build a pump with 18mm bore and 400mm stroke which I calculate will get my 25mm tyres to 85 psi in 70 or 80 strokes. If I use carbon tubes it will weigh between 100 and 150 grams which is less than many mini pumps.

The plan is to machine a plastic collar to slide down the inside the seat tube and fix to the upper water bottle fixing screw. The lower end of the pump will have a peg to locate into this collar - maybe even screw in. The pump handle will be machined slightly smaller than the inside of the seat post and will have o rings to make a nice rattle free fit - and give a bit of grip. So with care the pump can be removed and replaced without getting covered in grease.

Problems I have not yet resolved are if the carbon tube can take the pressure and if the inside of the tube can be made smooth enough to seal the piston. Also I haven't yet figured how to hook up to the inner tube valve.

I will keep you posted on my progress if you are interested and always appreciate your suggestions and advice - though it is unlikely anyone is an expert in this particular field.

Last edited by mikeread; 06-11-20 at 08:56 AM.
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Old 06-03-20, 04:03 PM
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Mike- I'm sure you remember the seat post pump that was marketed in the early 1990s. IIRC it was part of the budding MtB accessory field. We had one or two go through the shop and found the pumping action to be poor (but my standard was and still is a Zefal HPX...), the post was heavy and by current standards fairly short in length.

I think the idea is pretty cool but see some fine points which I'd want. First is some way to re establish the seat height (simple collar butting against the top of the ST?) . Second is a non rattle install. The pump needs to be tethered to the post so on removal it also comes out. The presence of bottle bosses further down the ST need to be dealt with. What ST ID would this be suited for?

I suspect that a CO2 device might be an easier creation compared to a pump. I believe there are a few such devices that are meant to reside in a BB or Steerer. Andy
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Old 06-03-20, 04:14 PM
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Disadvantage: Having to explain why you didn't just go with CO2.

Interested to hear how it works. Are you using a titanium post for more room inside? Wish I had the skills and equipment to try something like this, love DIY solutions.
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Old 06-03-20, 04:49 PM
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I think you are missing an opportunity here. Why not install the internals of a pump into the seattube with an external hose. Just loosen the seat binder bolt and use the seat to pump.
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Old 06-03-20, 05:32 PM
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These folks beat you to the punch:
seatpost pump

Scanning the comments of that link will prompt you on ways to optimize it further. Keep us posted!
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Old 06-04-20, 04:48 AM
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Steve - I tried carrying a CO2 inflator years ago but always carried a back up pump as well. I usually only get punctures 3 or 4 times in a year so when I ran out of cartridges I couldn't see the point of carrying both systems and have managed fine with just a pump ever since.

Also I lend my pump to people who failed with CO2 more often than I use it myself. So I have no plans to use it again.

There is plenty of room inside a carbon post. Having a long pump means you can keep the bore small to make pumping easy and still pump plenty of air. So a 20mm diameter tube is plenty and I have 22.5mm inside my carbon seatpost.

Duane I have seen that pump but it combines all the disadvantages of a mini pump with all the disadvantages of putting it in the seat tube. The main reason for going in the seat tube is to go long
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Old 06-04-20, 05:07 AM
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Andy I always mark my seatpost with a small square of electrical tape so getting it back in the right place is not a problem. I might make and fit a collar though just for the hell of it

There will be a collar inside the seat tube at the top bottle boss to stop the pump going any further and to centralise and secure the pump - with a spigot or a screw thread. The pump will go right up into the seat post (sliding fit with O ring to stop rattling) so when the seat post is removed the pump handle will be sticking out 100 mm or so. Seat post is 27.2 OD 22.5 ID

The plan is to get a pump in the seat tube that is as good as the Zefal HPX, I did consider just buying and modding an HPX (or similar) but then thought it would be more fun to start from scratch.

Cynikal That might work but there would be quite a few problems to resolve and it would be a maintenance nightmare. Also I am not keen on modifying the frame as it is already painted.
With this design you would need some sort of pipe connector between the frame and the valve which I am trying to avoid as it would reduce pumping efficiency. Also the pump bore would have to be 27.2mm which would more than double the pumping effort over my planned 18mm bore. This might make the idea more suitable for low pressure high volume MTB tyres.
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Old 06-04-20, 05:12 AM
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I would appreciate if a MOD could combine the posts on this and duplicate threads and delete the other threads - or is there a way I can do it?

Thankyou

Last edited by mikeread; 06-04-20 at 05:27 AM.
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Old 06-04-20, 10:33 AM
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Originally Posted by mikeread View Post
Go Long
Yes, I agree, I was just saying there are folks commenting on that pump and indicating what they would change and you might gain some insights into ways to make the first iteration the best it can be. Anyway, fun project.
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Old 06-04-20, 11:27 AM
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Originally Posted by Andrew R Stewart View Post
... First is some way to re establish the seat height (simple collar butting against the top of the ST?) . ,,,
3M has perfected the answer in all kinds to colors and styles. A small piece of tape. (From a guy who has built about 50 sailboats and used cases of 3M tape.)

Ben
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Old 06-04-20, 01:17 PM
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Originally Posted by duanedr View Post
Yes, I agree, I was just saying there are folks commenting on that pump and indicating what they would change and you might gain some insights into ways to make the first iteration the best it can be. Anyway, fun project.
I did follow your link Duane and read and watched some reviews. Thankyou
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Old 06-04-20, 09:00 PM
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Originally Posted by 79pmooney View Post
3M has perfected the answer in all kinds to colors and styles. A small piece of tape. (From a guy who has built about 50 sailboats and used cases of 3M tape.)

Ben
I also use tape to mark my post heights. But I am not removing my post other then annual cleaning. I'll also mention that I see tape that has moved for a number of reasons nearly every day at work. The adhesive on most common tapes does not really dry and acts like a lubricant if the tape is pressed on or stretched/shrunk. For a temporary mark it works well if not disturbed. Not what on the road work is best at.

I am reminded of what Sterling Moss once said about an up and coming young race driver. "He charges into corners like his brakes have never failed" Andy
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Old 06-05-20, 10:26 AM
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Originally Posted by Cynikal View Post
I think you are missing an opportunity here. Why not install the internals of a pump into the seattube with an external hose. Just loosen the seat binder bolt and use the seat to pump.
That's what I was thinking as soon as he started talking about machining plastic collars to go inside the seat tube

You could actually make an awesome pump like this. Rather than use the actual seatpost it might be better to have a thinner tube going down inside it. If you had a saddle with a cutout (as many do) this tube could somehow pop up through the cutout when required (and not when not required especially not when riding), the top could fold over to make a T handle and you would use it like a track pump.
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Old 06-05-20, 11:38 AM
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Making a long slim pump is rather simple. I would just make one from aluminum that is close to the length of the inside space from the interior of the seatposr to bottom bracket and have it butt up against a cork of some sort at either end to lock it in place from rattling. An adapter that links the pump to the valve should be easy enough to make and could tuck separately into your emergency tool kit. A T shaped piece could be quickly threaded onto the pump shaft for ease of use without needing to be part of the pump when it's slid in place.
I have made several simple pumps from copper plumbing pipes that will reach high pressure.
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Old 06-11-20, 08:49 AM
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Got in the workshop today and roughed out a few bits.

I expected to have a couple of attempts at making the piston but it seems to have worked first time. The design is copied from the pistons on a couple of mini pumps I have, a clearance fit piston with a tight fitting O ring in a 'cut away' slot. The principle is that the O ring seals on the push stroke but is not supported fully (by the cut away slot) on the pull stroke and deforms to let air past. I just used the nearest O ring size I had and winged it with all the piston and groove dimensions so I was quite pleased when it worked first time.

I am waiting for delivery of some umbrella valves before I can start on the business end of the pump.

For simplicity on the first one I might connect to the inner tube valve with a flex hose donated from another pump, this just needs a threaded hole in the end of the pump. I would like to do away with the hose and connect the pump direct to the valve but haven't yet figured how to make and fit a reliable sealing arrangement in the limited space available.

Hope you are finding this interesting - I am

For the weight weenies, weight so far 84 grammes



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Old 06-11-20, 09:32 AM
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Originally Posted by mikeread View Post
Got in the workshop today and roughed out a few bits.

I expected to have a couple of attempts at making the piston but it seems to have worked first time. The design is copied from the pistons on a couple of mini pumps I have, a clearance fit piston with a tight fitting O ring in a 'cut away' slot. The principle is that the O ring seals on the push stroke but is not supported fully (by the cut away slot) on the pull stroke and deforms to let air past. I just used the nearest O ring size I had and winged it with all the piston and groove dimensions so I was quite pleased when it worked first time.

I am waiting for delivery of some umbrella valves before I can start on the business end of the pump.

For simplicity on the first one I might connect to the inner tube valve with a flex hose donated from another pump, this just needs a threaded hole in the end of the pump. I would like to do away with the hose and connect the pump direct to the valve but haven't yet figured how to make and fit a reliable sealing arrangement in the limited space available.

Hope you are finding this interesting - I am

For the weight weenies, weight so far 84 grammes



it is certainly pretty
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Old 06-11-20, 10:48 AM
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Could you tap the pump end to a presta thread or tap the pump end to fit a schrader thread and then use an adapter to link to a presta?
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Old 06-14-20, 06:57 PM
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Foot pump in a post.

https://www.ternbicycles.com/us/gear...mp-20-seatpost
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Old 06-15-20, 07:53 AM
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Originally Posted by wsteve464 View Post

This will not fit in a 27.2 seat tube and weighs a whopping 718g. I presume this includes the seatpost but even then it is a bit of a lump.

It is much more fun to spend hours - and a small fortune making something that may not work - but looks nice and weighs very little
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Old 09-16-20, 10:25 AM
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I have got back onto this project recently and now have all the bits machined and ready to assemble.

For simplicity I will start with a flex hose from another pump, The end plug is removable so I can get at the valve plate if it needs modifying, this also means I can make a new end at some point for a direct fit to the valve. I haven't figured out how to do this yet!


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Old 09-17-20, 01:10 PM
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Put it all together today and gave it a whirl and .............. it didn't work !

If I put my finger over the end it builds pressure nicely but when I pull the handle out, it pulls back in a bit, so I suspect the piston is not letting air past easy enough on the return stroke.

I was a bit unsure of the piston and just jammed it in place with some tape, for easy removal, so will have to pull it off and try some modifications.
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Old 09-22-20, 05:08 AM
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After messing with the piston and o-ring I decided the o ring must be too tight a fit around the piston, preventing air from flowing easily into the cylinder on the pull stroke. So I made a new piston with a very loose o ring. No joy, exactly the same problem!

Had a re-think and wondered if the handle end bushing was not letting air in easy enough, it was not a particularly close fit so I had assumed this would be OK. Machined a couple of slots to let air in and problem solved

Pumped my tyre up to 70 psi in 60 strokes. I don't ever pump higher than 70 but took the pump up to see what it could do, at about 85 psi air started blowing back past the piston. I suspect this might be because of the now very loose piston o-ring, so I need to make piston number 3

You would think a pump would be quite simple to make - Getting there slowly
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