Lezyne Floor Drive pump - piston/shaft seal (o-ring) sizes

[Suffolker]

I have a Lezyne floor drive pump (the model with the steel barrel), which needs to have the two interior piston o-rings replaced (the one that fits around the end piston itself and the floating shaft one).

These have been in the pump from new, and have at last started to give out. I think also that they are sightly distorted by age and use, and I'm reluctant to use them as size indicators unless I have to.

There appears to be a kit available for repair, but this seems to have only one o-ring and is very hard to get hold of at the moment (in the UK). I wonder therefore if anyone has got the exact measurements (ID X OD x section (diameter)) of these o-rings. I have seen that o-ring failure is a prime cause for these pumps to cease working, and I'd like to have a few handy in case of need. It's also the case that good quality nitrile or viton rings aren't cheap, and I don't really want to buy a "scatter gun" range in hopes of hitting the right ones.

I've looked around the web for these dimensions, but so far haven't been able to find anything definitive.I am led to understand that these spare parts are common across the floor pump range.

[Brucey]

daft question this, but have you tried a little lubrication of these O -rings? Often they wear faster and start to leak when they are a little dry and normal service can be resumed (for a while at least) once fresh lube is applied.

SJS have some Lezyne seal kits (but not floor drive ones); might they know the sizes or if the particular seals you need are included in another kit?

cheers

[Suffolker]

daft question this, but have you tried a little lubrication of these O -rings? Often they wear faster and start to leak when they are a little dry and normal service can be resumed (for a while at least) once fresh lube is applied.

SJS have some Lezyne seal kits (but not floor drive ones); might they know the sizes or if the particular seals you need are included in another kit?

cheers

Thanks for your reply.

I have lightly greased them, using plumber's grade clear silicone grease. Although it does improve them slightly, they are definitely on the way out. Air bypasses the seal, so often (but not always) a full downward stroke has no air pressure resistance, and no air delivered at the chuck. Uncommonly for me, I haven't manage to do something stupid like tread on the barrel and ovalise it, either.

SJS have something called "Lezyne Plunger O-Ring & Flip Chuck Connector for HP Floor Pump", which is out of stock, and is the kit with one o-ring only, and other bits which I wouldn't expect to need. I will, as you suggest, make enquiries of them regarding size. As I mentioned earlier, frequent o-ring failure seems to be a real problem (from the gripes around the web), along with a degree of unresponsiveness from Lezyne. I have dug up some design drawings of others of their pumps, which have seal dimensions, but there appears to be nothing similar for these models.

[rjb]

Why not disassemble the pump, carefully remove the "O" rings and measure them. Lidls currently have sets of "O" rings on offer in there stores, metric or imperial but they may be identical size wise

[Suffolker]

Why not disassemble the pump, carefully remove the "O" rings and measure them. Lidls currently have sets of "O" rings on offer in there stores, metric or imperial but they may be identical size wise

That's what I may have to do in the end, although I'm never happy sizing from used or worn o-rings. The piston seal as usual sits in a groove, is a pretty tight fit, and has to be prised out when removing it. That can alter the dimensions quite significantly, however carefully it's done. The other method I'd use (probably as well), is to micrometer-measure the OD and thickness, but getting the ID is tricky. I would expect the ring to be a standard size, and probably metric, so it would then be a case of the logical closest size. I'd guess that a .5mm difference either way would dictate whether it holds air pressure pumping, or be immovable in the barrel.

I was rather hoping that someone else had been this way before, and knew these important measurements. I'm a bit out in the sticks here, and unfortunately the last "proper" engineers supplies outfit, where in the past I could cart along machinery of all sorts and check it out against their enormous stocks of rings, seals, bearings etc. etc. has shut up shop. It'll likely be a case of sending away for the things.

[Suffolker]

I've worked out what I think is the correct size, and have some rings en-route. These aren't anything special (e.g. Viton) but if they are the right ones, and work OK, then I may spring for some of better quality.

I'll report the results here next week.

[PH]

I'll report the results here next week.

Please do, I have the same pump that sometimes works and sometimes doesn't. was waiting till someone had the kit in stock but if I can avoid that all the better.

[Suffolker]

I'll report the results here next week.

Please do, I have the same pump that sometimes works and sometimes doesn't. was waiting till someone had the kit in stock but if I can avoid that all the better.

Not too financially onerous if I'm wrong, at £2.50 per half-dozen post paid. If I'm right, then I'll be well in hand for stocks. The £2.99 SJS kit is an odd thing, as I can't see why it would be necessary to replace the flip chuck connector (per SJS, but described on Lezyne website as a "replacement swivel") unless the thing has been damaged somehow, perhaps by cross-threading.

[Brucey]

BTW it is as well to know how an 'O' ring seals when it is used as a plunger seal; when the pressure is applied, the O-ring bears/seals against the upper face of the plunger and (of course) the bore of the barrel. The part of the seal between these two contacts sees atmospheric pressure only. When under pressure, it is the pressure itself (around the remaining ~270 degrees of the ring section) that forces the seal into position, and indeed the higher the pressure, the better the seal becomes.

So you can see that

a) you definitely need good lubrication (high pressures give high seal loads) and
b) you need some kind of a seal to start with, else the pressure cannot develop in the first instance.

On the latter point the seal must be preloaded in some way; typically the OD of the seal is fractionally larger in diameter than the barrel bore, and the width of the groove in the piston is narrow enough that the seal cannot 'wrinkle' too much due to this preload. Often the O ring is slack on the ID of the piston groove and the underside of the piston is perforated, so that the air can bypass the piston seal easily on the return stroke.

Once the seal is worn often you can 'catch it' at the top of the pump stroke and thus make the pump work OK, but you are living on borrowed time this way; a little more wear and the seal won't catch any more. If you get to this stage and you are really stuck you can sometimes cut some thin brass (or steel) shim (in a strip slightly narrower than the O ring section) and fit it coiled up inside the O-ring; this can help a worn O-ring seal against the barrel bore for a while longer. Also in the last chance saloon is deliberately using a little lubricant that will make the seal swell; a few drops of ATF will often do it.

All pumps I have ever owned that use an O ring as a main seal have suffered wear on this part, far sooner than I'd like. I do not think that Silicon grease is a very good lubricant, (it is probably little better than Vaseline in this instance). Of course many oils and greases will attack either the pump seal or the inner tube, so you need to be careful. Of the lubes I have tried the easiest/best to date has been '151' brand synthetic spray grease; this doesn't dry out too quickly and is specifically described as being suitable for most rubbers and plastics; it hasn't attacked any that I've used it on so far.

On balance I think that the old (SIlca etc) approach of using a leather cup washer is actually a pretty smart method; heat -which is a necessary consequence of vigorous pumping- doesn't degrade the seal quality (unlike any plastic or rubber seal) and a new seal is easily fitted should it eventually fail.

cheers

[Suffolker]

@Brucey

I always think a day wasted if I learn nothing new. Today, I have about a week's forward credits, at least as pumps are concerned. I shall also be applying this new knowledge to the problem at hand.

On your last point; my favourite footpump is a folding-foot "Shelley" model in steel, with wooden handle and leather cup washers. My grandfather had it as his car tyre pump before the last War.
It pumps like nothing else, and, as I read your last posting, it strikes me that the durable solution is to get a new delivery hose and chuck on it, and use one of the tyre pressure gauges supposedly superseded by "on-pump" gauges. At present, I use it only on my one Schraeder valve machine.

Altogether fascinating.

[Suffolker]

Some more observations on this.

Firstly, I don't think that I'd try to remove the plastic top cap with anything other than a correctly-fitting pin spanner. The threads, which are about 3/4" or a bit more in length, are very fine, and, on my pump at least, a fair amount of force is needed to unscrew it. Once it's about halfway unscrewed, it's possible to then grasp the cap with a rag and do the rest by hand. I've seen people say that they've removed the cap with needle nose pliers and similar tools, but it strikes me as being very easy to mash up the cap, and also damage the shaft.

Having got it apart, inspection showed a lot of blackened grease in the plunger area. The colour is a wear product from the o-ring, I suppose. The grease had also choked the movement of the o-ring (something which Lezyne advise you check/prevent in their floor pump repair Youtube video). I cleaned it all up, and thought I'd test it with the original o-ring. The pump performed a bit better, with more pressure from the top of the down-stroke, but still nothing to write home about.

Meanwhile, I had obtained a (10 for £3.50) rubber o-ring, 22m ID x 3mm thickness (section). This fitted fine in the plunger groove, being slack and rotatable. Compared to the original, it looks a trifle "plumper", probably because it's new. It also required a little more cajoling into the barrel, but not much. I didn't put any more lubricant on the ring, as I reckon there was already plenty in the barrel bore (from sticking a finger in the top and from the amount on the first o-ring, before and after cleaning).

I've now deflated and inflated several Presta and Schraeder tyres, and the pump is much better. It delivers air more easily and the pumping pressure seems increased. There's no unpressurised downstrokes, with the handle flopping from top to bottom, even without a hand on it.

So far, so good. Other than "rubber", the composition of the replacement O-ring wasn't specified. I'll see how it holds up in use, and, although I've plenty of spares, I have a feeling it might pay to use a specific composition of o-ring, perhaps nitrile or Viton, as these are usually more durable, although a bit more expensive.

Edit:-
A little more investigation reveals that the o-rings I bought are indeed nitrile rubber, so I'll stick with them pro tem. I also find that there is no advantage in using the more expensive Viton for this application.

[Bnystrom]

For anyone who is "metrically challenged" in the US or elsewhere, these o-rings are 1 1/8" x 7/8" x 1/8", also known as a #27 in the plumbing trade. I found them at a local hardware store for $0.47 each.