Track Pump Connectors

[Mick F]

I have three different ones ....... would you believe!

From L to R they are:

Auto Dual Valve that came with my Serfas track pump.
Topeak Twin Head I bought some years ago is in use regularly.
Original Silca that I still have from my Silca track pump that bit the dust years ago.

My problem is that it has appeared that my tyres have been losing pressure rather too quickly. I have been topping them up every couple of days even though I have Schwalbe inner tubes.

Because of another thread on here, I decided to experiment. I inflated my tyres as usual but monitored with a seperate pressure gauge ............ only to find that my tyres DON'T need topping up every few days.

That gave me an idea to experiment with the three pump heads I have.

The Auto Dual Valve I have never liked, that is why I went for the Topeak Twin Head. I fitted the ADV and had a play with a spare wheel. It inflated fine but was a devil to take off the Presta valve. I really have to tug. Also, when you release the lever, air escapes whilst you pull.

The TTH is fine for fitting and removing, but when you operate the release lever, air escapes just like on the ADV. If I were to leave either of these heads on with their levers released, the tyre could probably completely deflate.

When fitting both the ADV and the TTH, the pressure gauge on the pump reads the pressure in the tyre. This proves that the Presta valve is depressed allowing air from the tyre into the long hose and up to the gauge. There isn't a continual release of air due to some sort of one-way valve in the pump when fully connected.

There must be some sort of "half-way house" when disconnecting these heads insomuch that the Presta valve is still depressed but air escapes from the connector because it's not locked on and sealed.

Here's the big difference............

When I fit the Silca head, the pressure gauge doesn't move. There is no release of air when I connect. The pump works perfectly of course, and when I'm up to pressure, I just pull off the Silca head. The only air released is from the hose and pump.

Therefore, from now on, I'm using the (maybe 25 year old) Silca head.

Any comments please?

[531colin]

When you connect your (low volume) tyre to the dead space in a track pump hose, the pressure equilibrates causing a drop in the (measured) tyre pressure.
Now that you are checking your tyre pressure with a separate (low volume) gauge, surely it doesn't matter what track pump head you use, as you will only be connecting it when your tyres really do need topping up?
(I suppose to really answer that you need to find a way to measure if the puff of air when you release the connector significantly changes the pressure in the tyre .....even if it does, I would just use the most convenient connector, and over-inflate to compensate for a loss of pressure on dis-connection.

[Mick F]

What I do normally, is connect the pump and then see that the pressure has dropped, then pump it up to the correct pressure, then remove the pump.

Had I not connected the pump, the pressure would have been fine, but I didn't know that.

I'm saying that the very connection of my pump releasing air and it gives the false impression then my tyre needs inflating, so I inflate it. The very disconnection allows air to escape from the tyre thereby exacerbating the problem and I end up with less pressure than I thought I had.

Connection and disconnection loses air from the tyre due to the design of the Topeak Twin Head and the Dual Valve Head.

Using the Silca head, this doesn't happen.

[gaz]

.

[ChrisButch]

Some time ago I replaced your R with your Middle on my Silca pump. I too find the Toepeak much better, despite the small problem you mention. I got fed up with the Silca brass chuck because, with no locking mechanism, it would start to leak air while inflating once there was a small amount of wear on the rubber seal. You needed a third hand to hold it on straight while pumping. It also tended to bend the weak threaded brass spindle at the top of the valve.

[CJ]

Therefore, from now on, I'm using the (maybe 25 year old) Silca head.

I hope you can still get new washers for it, because they're going to wear out. I have that problem with the original head on my old SKS Track Pump. New washers are like hens teeth, and they wear out fast because the high-pressure rush of air from the hose upon it's detachment blasts bits of rubber off its edges!

The Topeak TwinHead I had on another pump (now broken) didn't wear like that, perhaps because that one released the hose pressure momentarily before detaching from the valve. Maybe that lost a bit of pressure from the tyre too, maybe not if I did it quickly, but if it did it was a teeny bit of pressure because when I checked after pumping the tyre was near enough at the same pressure I thought I'd put in, allowing for the fact that none of these gauges are particularly accurate. What I do know for sure is that head didn't consume washers like there's no tomorrow. When I run out of SKS washers I'll be transferring the Topeak TwinHead to the old SKS pump - even though its gauge now under-reads by at least half a bar.

The failed Topeak pump originally came with their Smarthead. Like your Serfas Dualvalve it's not just smart but too clever by half. It failed within one year. I mended it, but that fix lasted only for a few more months, so I got the TwinHead to replace it. That seems one reliable piece of kit.

[mjr]

Does the pressure drop consistently? If so, then 531colin may be right.

My pump has an ADV but I doubt it's responsible for all 20psi loss in a week and a bit.

[Mick F]

Does the pressure drop consistently? If so, then 531colin may be right.

Yes it does, but 531colin isn't right with respect to my problem.

I'll try and explain better.

Up until today, I used my track pump with the Topeak Twin Head and have used it for years.
I habitually connect my pump to re-inflate my tyres in the belief that they have gone down. I do this every couple of days.

Connecting my Topeak .......... initially on connection it allows air out of the tyre NOT into the pump. The air comes out of the other port on the head.

When connected AND with the lever locked over, the air in the tyre equalises with the pump and the gauge reads. Everything is sealed and there is no more loss.

It appears that the tyre has less pressure now, because it actually has! Had I not connected at all, the tyre would probably have been fine.

I pump up the tyre to an indicated 120psi.

I release the lock on the Topeak and air is released from the pump hose AND from the tyre via the other port. If I'm very quick, the tyre doesn't lose too much, but it still does lose some.

Therefore I'm subjected to a double wammy.
Lose air out of the tyre as I connect, and lose air again when I disconnect.

Using the Silca - notwithstanding the washer problem - connecting does nothing to the air at all. No air comes out to equalise anything. By pumping, it isn't until the pressure in the pump gets to the pressure in the tyre that the Presta valve lifts and the system equalises. On disconnection, the air escape is only from the pump and not from the tyre.

Maybe to cure the Topeak problem it needs the other port sealing off. When the lever is in the central position, both ports are open allowing air to escape from the non-connected one. It isn't until the lever is over that the other port is switched off.

You cannot pull the Topeak head off the valve until the lever is central, and within that finite time that you have to tug to get it off, you're losing air from the tyre. Ditto when connecting.

I know this isn't much.
I know it isn't a problem.
Trouble is, I was adamant that my 23mm 120psi tyres would lose 10% of their pressure in a few days. This is patently wrong, but I didn't know.

Now I know better, and I'm sharing my thoughts on why I was wrong.

[[XAP]Bob]

If you push the lever all the way would that stop the leak and allow you time to release the valve?

[Mick F]

Nope.
In order to connect or disconnect, the lever has to be central. When it is central, both ports are connected together so the air comes out of the Presta valve and goes straight out of the unused Shrader port.

I was just in the workshop experimenting .............

Connect the Topeak Twin Head and track pump to an unscrewed Presta valve on a tyre with loadsa pressure in there. Don't move the lever and the tyre will deflate .............. or it does with mine.

Therefore you lose pressure every time you connect and disconnect even if you're quick.

[Mick F]

Another experiment, and hopefully someone else can try this too.

Put the Topeak on the end of its hose into a bowl of water with the lever in the central position.

Pump away and watch where the bubbles come out.

With mine, the bubbles come out of both ports proving that the centralised lever allows both ports to be connected.

I would reckon that a better design would be for neither port to be connected with the lever central. Perhaps mine's defective?

Anyone else like to try this?

[mgronow]

Hi Mick,

Ive got the topeak head too and have often wondered about this exact problem. I was wondering though is the loss of air on disconnecting is actually pressure from inside the pump and not the tyre. Does the tyre actually go flat if you leave the head on the valve and turn to disconnect? I'll try this later...


regards martin

[[XAP]Bob]

Another experiment, and hopefully someone else can try this too.

Put the Topeak on the end of its hose into a bowl of water with the lever in the central position.

Pump away and watch where the bubbles come out.

With mine, the bubbles come out of both ports proving that the centralised lever allows both ports to be connected.

I would reckon that a better design would be for neither port to be connected with the lever central. Perhaps mine's defective?

Anyone else like to try this?

Not defective - mine does the same, but the small volume of gas I lose isn't very significant, despite my small wheels.

[Mick F]

Does the tyre actually go flat if you leave the head on the valve and turn to disconnect? I'll try this later...

Mine does.

That's the problem.

[The Mechanic]

I have a Joe Blow pump with the very twin head that Mick has. Two things are different with mine;

1. I do not get a reading on the pump gauge before I start pumping. This is because the valve on the tube is still closed.
2. I do not lose pressure from the tyre when I disconnect. The only air that is released is that in the pump and hose. This is because the valve in the tube is closes when I stop pumping.

There is a simple and logical reason for Mick's problem. Mick is obviously pushing the twinhead too far onto the valve, thus depressing the presta valve. If you try pushing the head onto the valve just enough to engage the clamp when you twist the lever, all your problems will be solved.

When I pump I can hear the valve stem ticking as it opens and closes with each pump stroke. This has always been the case since I can remember.