Does this cap have an o-ring or gasket in the bottom to seal out the water so the regulator can be dunked to clean? And if so, is it captive in such a way that it won't come out if the cap is not threaded to the reg (while diving) and free-floating in the water?
No this does not have an o-ring. It is not recommended to dunk a regulator unless it is under pressure as you don't want water getting into the first stage.
there is no O ring, the cap is long enough that it goes past the threads and creates a seal. I have never had a problem with leakage while rinsing. the string that you see in the picture attaches to one of the hoses.
the o-ring is on the male end . I have been waiting for these for a while. O-rings v=disappear. carry spares.
The cap, indeed, has a thick hard rubber or plastic ring that serves as a seat for regulator's o-ring. It is seated there firmly, does not fall out. While it seems to be designed to seal the high pressure inlet of the first stage, it is hard to tell if it absolutely prevents water from entering it. I just use it as protection from dust, and always soak regs in fresh water while pressurized (connected to a tank). Otherwise water would find a way inside. For the price the cap is very well made and does protect the reg, I think it is a must have item for DIN gear.
This cap is for DIN. The O-ring is in the regulator not the cap. It seals when you screw on the cap the same way it does when you screw the reg into a tank valve.
I have these on two of my DIN regs and just looked inside and there is no o-ring or gasket. However, I have been dunking my reg with these caps in rinse tanks for several years and never noticed any water leaking in. There is a smooth surface in the bottom where the regular will ground out on the cap bottom. Also there is about 8 threads. So at atmospheric pressure it is doubtful that water will leak in -- it hasn't for me.
No, it seals against the DIN O ring. I've used this for several years, and have never had a problem with leaking.
This cap does not have an o-ring or gasket in it but it fits, screws, on to the first stage (DIN) threads very tight and keeps the water out when rinsing and even soaking in a rinse tank. No need to worry about the o-ring or gasket coming off as there is none. This cap works well for me!
It does not have an o-ring. When screwed down it forms a tight enough seal to keep fresh water out when dunking to clean.
DIN regulators have their own captive O-ring, so none is necessary for this regulator cap. In short: yes you can dunk your regulator with this screwed on and it will stay dry. The cap itself, if left on the first stage while diving, will get wet. I always attach mine to the stainless screw-in tank plugs and leave it on the boat. Hope this helps.