Efficient track pumps?

[Brucey]

I recently went to use one of my track pumps and I noticed that there was quite a lot of resistance just pushing the handle down briskly, even when I wasn't pumping a tyre up.

Some of the drag is in the piston (and will vary with the pressure, because of the way the pressure loads the seal) but much of the resistance was just pushing air through the many connections and fittings. The pump is of a fairly modern design, meant for low pressures with a large piston, with a short hose (of the flexible rubber type rather than the reinforced type) leading to a gauge mounted on a separate clamp round the pump barrel, and another hose leading from a swivel fitting there to the air chuck. Delving in the pump internals revealed that there were many possible constrictions to the airflow (exact sizes tbc).[edit: the pump barrel is 36mm and the bore reduces to 2.5mm in the barb fittings]

1. transfer port ( from the side of the barrel )
2. Check valve
3. Hose barb fitting insert (HBF) with ~2.5mm bore
4. Hose (~5mm bore)
5. HBF
6. transfer port into gauge mounting
7, transfer port into swivel coupling
8. HBF
9. Hose
10. Barb fitting onto chuck
11. transfer port into chuck
12. chuck insert.

Some of these were partially blocked; eg because of burrs/flash on the mouldings or #11 because the port didn't line up perfectly with the opening in the moving parts inside the chuck. The transfer ports were not well designed, with lots of right angles in the flow path, but at least they had a reasonable flow cross section.

But each HBF had a small bore constriction and worse than that #3 and #8 have a flat surface with a plain hole in it on the entry side, i.e. there is no concession to smoothing the 'organised flow' that is required as the air enters the fitting. [ it is normal to have a smooth entry radius in a flowpath; it is less important on an exit though, hence carburettors often have carefully shaped bellmouths at entry, but similar devices are not usually fitted to exhaust pipes}.

So after a bit of fettling I made some small improvements to the flow path, making better radii and clearing obvious partial blockages. When topping up a high pressure tyre most of the effort put into the pump is against the pressure forces, not the flow forces, so in a traditional track pump some constriction in flow is not a big deal. But when inflating a high volume tyre from flat, the situation is reversed; until the tyre is up to pressure most of the effort (esp when pumping briskly) is expended against flow resistance not pressure resistance; the large piston in this pump made it more obvious than normal. Some tyres never get to a high pressure (eg fat bike tyres). Other tyres (eg car tyres) have both high volume and fairly high pressure (30-40psi). I expected to be able to pump a car tyre up with this particular pump; in fact I found it hard work right from the start, in good part because of the flow resistance.

Has anyone else noticed similar things? Are there pumps out there which are better designed for high volume flow?

cheers

[peetee]

I can't answer your question but do have to ask, have you read any publications by David Vizard?

[Brucey]

I can't answer your question but do have to ask, have you read any publications by David Vizard?

yes, I have. I also have some background in fluid dynamics...

cheers

[Mick F]

I can't answer your question but do have to ask, have you read any publications by David Vizard?

I had his book, "How to Modify your Mini" some years ago.
https://www.amazon.co.uk/Modify-Your-Mi ... 0863430414

I bought a 1275cc Alegro A+ engine and had it bored out to 74mm = 1400cc. A chap I met down in Plymouth who has done many many A series mods, ported out the cylinder head with the biggest valves he could fit. I did all the rest as well as fitting a Road/Rally Piper 274 camshaft and fitting twin inch and threequarter SU carbs with KN filters. Competition clutch, oil cooler, bigger radiator and electric fan, and extra engine stabiliser mounts.

Had it rolling road tuned and it produced 100bhp. Went like a rocket.
Sold the lot eventually, and the Vizard book as well. Should have hung onto the book as I could have sold it a good profit.




As for a the track pump, I've only had high pressure ones and no complaints especially now I have a Lezyne one. Knocks spots of the others, even the venerable Silca.

[Samuel D]

I’ve noticed the phenomenon but haven’t used enough pumps to see if differences in flow efficiency are worth looking into. If anyone has sought to improve this deliberately it might be Josh Poertner’s Silca.

Incidentally, last night I timed how long it took me to inflate a 25 mm tyre with a Zéfal HPX. I got 100 full strokes – good for about 80 PSI, I think – in 45 seconds with vigorous but reasonable pumping. The speed of the first few dozen strokes was more hindered by pressure build-up from flow restriction than tyre pressure.

[De Sisti]

HBF

[Samuel D]

HBF

Brucey explained this TLA where he first used it.

[Brucey]

Incidentally, last night I timed how long it took me to inflate a 25 mm tyre with a Zéfal HPX. I got 100 full strokes – good for about 80 PSI, I think – in 45 seconds with vigorous but reasonable pumping. The speed of the first few dozen strokes was more hindered by pressure build-up from flow restriction than tyre pressure.

that's useful to know. The HP/HPX has a slight flow resistance mainly because of the check valve (which is well designed by comparison with many, even if it does make the pump sound like an asthmatic pigeon at times). For some years I wouldn't use an HP/HPX because when racing I'd need to inflate a spare tub as quickly as possible/practicable; the HP/HPX had two flaws in this respect; the check valve and the small barrel.

I used to use a Silca frame fit pump instead; no check valve and a fatter barrel meant I could expect to inflate a tyre from flat in less than fifteen seconds of frenzied pumping. Unless the valve got jammed open of course, in which case the pump handle would be launched into space by the air-powered mortar thus created.... The HPX is a much safer bet.

Incidentally 100bhp is 'plenty' in a Mini. I used to break transfer gear bearings (even in A+) with less. Two 1-3/4" carbs is more than enough for that power BTW; a single carb of that size doesn't really hold the engine back even at 80bhp; some folk reckon that twin 1-1/2" carbs are the best choice for about 100bhp.

cheers

[rjb]

I was given a high volume track pump after it was left in a garage during a house move. It has a pressure gauge which goes up to 160 psi. The most I can get out of this pump is about 50 psi. And it's hard work. Time to strip and investigate. Thanks Brucey it's niggled me for years but time to investigate in an idle moment. It's a Beto Monza labelled as a cycling necessity.

[Samuel D]

If you pump slowly enough, as you will by necessity when it becomes hard work, the flow restrictions discussed don’t matter. In other words, these restrictions won’t limit attainable tyre pressure (ignoring marginal dynamic effects*).

Perhaps your Beto Monza used the same pressure gauge as another model aimed at higher pressures (with a lower volume per stroke), much like car models often share a speedometer across the engine range. I wouldn’t expect to get much more than 50 PSI out of a high-volume pump anyway.



* While at someone’s summer house in June I inflated the tyre of a tiny child’s bicycle with the only pump available, a cheap track pump with a locking lever for the valve stem connection. The lever could not be brought up because the wheel’s hub got in the way. I held the head against the Woods valve as best I could and pumped for all I was worth with the other hand. Despite the massive leak rate the tyre got inflated. In that situation, better flow would have increased the maximum achievable pressure in the tyre.

[Brucey]

I just measured the bore of my low pressure pump and it is 36mm, i.e. about 1.42" dia. This gives 1.58 sq in area, thus it would take a load of 158lbs on the piston (neglecting friction) to achieve 100psi. Realistically I can't get more than about 60psi out of this pump, so either I'm weakening or the piston gets super-draggy under pressure. The piston seal is a (fattish) floating 'O' ring; I'll try greasing it better and see how that goes.

Traditional track pumps have a smaller bore. If this is (say) 27mm this gives an area of 0.89 sq in. Thus (neglecting friction) the load required to get to 100psi is a much more reasonable 89lbs. If the piston is 25mm then the load diminishes to a still more reasonable 76lbs.

In round numbers the 36mm bore shifts air at twice the speed (and twice the load) vs a 26mm bore pump.

cheers

[rjb]

As I am a 126 lbs climber that explains why I can only achieve 50 psi. My pump has a similar barrell diameter to yours.
Describing this pump as a cycling necessity is somewhat misleading

[Nigel]

Incidentally 100bhp is 'plenty' in a Mini. ………...

Ah, so you've not been watching "Project Binky" on YouTube for the last five years.....

As for the track pumps, can't really help, not enough experience of different types. The two I've owned have been OK.

[gaz]

Thirty years ago I bought a Zefal Double Shot track pump. Current equivalent here.

Designed to pump on the down stroke and the upstroke (IMO a gimmick rather than a useful feature), it certainly shifted a large volume of air on the down stroke.

Ten years ago it gave up the ghost, I switched to a Topeak JoeBlow Sport. My anecdotal reflections at the time appear below.

Compared to the Zefal the barrel size is much smaller and it pumps less air per stroke. Whilst it takes more strokes to pump to pressure each stroke seems to take less effort.

Worth bearing in mind that the anecdote was based on the brand new Topeak versus the twenty year old and unserviced Zefal.

If I had found a Double Shot for sale at the time I'd have bought a second.

[slowster]

I've a 30+ year old Zefal Plus, which has two barrels: 42mm diameter and 26mm diameter (for which incidentally Zefal still sell a pair of the rubber washers for the princely sum of €2.95 plus P&P). I've never noticed how much flow resistance there is, but the two stage compression seems to be quite quick/efficient.

Unfortunately I damaged the gauge when I overpressurised a tyre to try to get it to seat properly on some Kinesis wheels (which I suspect have rims which are either badly designed or out of manufacturing tolerances), and I've been meaning to remove the gauge and measure the threads in order to see if I can buy a replacement.