My air pumps are all made for Shrader valves. My bicycle tires have Presta valves. I recently purchased six adapters and the package came with six caps to fit a Shrader valve. So this makes me ask: Do people leave the adapter on the tire valve? I have been installing the adapter to fill the tire and then removing it.

I recently bought a pair and just leave them on for now.
It just makes it quicker to top off with my pancake compressor when I have a quick errand.
When I'm riding more miles (summer) I don't use them. I use my floor pump. Kind of a miles ridden/effort kind of thing.

I remove it because I dislike the appearance.

I have a road bike with schrader and another road bike with presta. My old mini pump has a hose to attach to the valve (schrader only). I keep the adapter on the hose so I always have it. I agree it looks a bit dorky on the stem, more so with a cap on it. I have a floor pump that does both.

If you bought your pump recently (like in the last 10 years or more), it may be both.

If your pump has a plastic cap on the end that clips on the valve and it unscrews, it may be reversable.

You certainly can just leave it on but if you notice that your open presta valve is leaking (it shouldn't if working properly) you may have to remove/replace the adapter and screw down the presta valve to stop the leak.

If the stem is a bit long sticking out from the rim, the tongue weight of a brass/alloy adapter might not be healthy for the stem under duress situations.
If I need to use an adapter or extender, I remove them & stow them in a small ziplock bag in a seat bag.

A proper bike pump should be able to do both or will likely just do Presta valves. I use adaptors for emergency situations because I want a pump that works well for my tires and is easy to use. Having to potentially unscrew the cap, then adaptor, loosen the valve on the tube, screw back on the adaptor, pump, unscrew the adaptor again and then tighten the valve on the tube and screw the adaptor on again and probably put a cap on that, is a huge pain. I would rather just loosen the valve, pump tighten valve and done.

I will also note that using an adaptor can unscrew your valve cores so if you are using them regularly you will want to have a valve core tool as well to make sure things are tight. It is a good tool to have anyway but way more needed with regular adaptor use.

I would get a JoeBlow Sport III and not worry. They are not expensive, very reliable and you can get parts for it if needed be. It has a presta side and a schrader side so you can do all valves (including Dunlop. We have sold them for years now and haven't had any issues and it is a quite easy pump to use, we use it as a shop pump as well. It also comes with a ball and bladder needle so you can pump balls and pool toys and such.

BITD, the Presta adapter was threaded onto the DT shift lever clamp bolt (or double down tube cable stop clamp bolt). The threading was the same and it kept the rarity/ mystique aura going on the exotic, skinny Presta valves. As the brazed on pivot became ubiquitous, storing the adapter on the valve stem became de rigueur.

It seems you are adamant to work with the prestas.

Considering air pumps are not expensive, it can save you a lot of grief by just getting a presta pump and then you do away with those silly things.

I work with a lot of donations of old bikes at a non-profit shop and I see adapters on Presta valves come in maybe once per season. Never seen them with caps (and we see a lot of quirky caps).

The amount of stress on the valve stem from the added weight of a Schraeder adapter is approximately zero from a significance standpoint.

this is my adapter. not for everyone, I admit

I like to leave them on my bike, but eventually they get lost.

My old theory was that if I ever have to air up at a gas station, or perhaps borrow a pump, I'd have the adapter. But in reality, that really never happens, and gas stations have been removing or hiding their air hoses.

I have, on occasion, worn out mini pumps, which one usually discovers when one needs them.

You can purchase push-on presta adapters. I haven't used one for years. In theory one attaches the chain to the pump, and it stays with your pump.

Adapters for Presta valves could also be screwed onto Campy (preferably) toe clip mounting bolts.

https://www.cyclebrother.com/cycling...823c-100-mm-fv + https://www.ebay.com/itm/192074494859 though.

Just making sure you don't confuse a cosmetic dirt cap with the threaded brass cap on the valve that must be turned shut after inflated.

Not strictly true; I remember that, back in 1965 or so, a few local racers would deliberately break off that brass nut and the portion of the valve inner core that extended above the outer valve body. Doing so guaranteed that they'd be able to inflate their sew-up tires with a Silca frame pump without risking inadvertently nudging the brass nut sideways and thus releasing all the air that they had just laboriously pumped into the tire.

As Silca pump users know, that instant rush of pressurized air out of the valve and into the pump would result in the pump handle blowing out of the pump body and flying across the street. Hilarious sight, if you weren't the one using the pump.

The only downside to snapping off the brass nut and top portion of the inner core was that the tire would have to be kept at or above a certain minimum pressure or else the inner core would disappear irretrievably into the tube. Training sew-ups with butyl tubes would hold their pressure for a pretty long time, but racing tires with latex tubes would have to be pumped up at least every few days, or else.