There is no key mechanism on the gas sampling bulbs. These are intended for use at atmospheric pressure. The maximum psi has not been established. The way to keep from breaking the glass is to not overfill the apparatus.
Directions for filling a Gas Sampling Bulb and Making a Standard:
I. Flush the bulb with clean helium or nitrogen before collecting the sample.
a. Open both stopcocks and flow at least on 1 1/2 to 2 bulb volumes.
b. Close the outlet stopcock, then the inlet stop cock after turning the gas supply off.
c. If pressure cannot be controlled then try the following:
i. Attach a 1-2 foot piece of tubing to the outlet of the sampling bulb.
ii. Close the inlet stopcock, then very quickly close the outlet stop cock (the tubing on the outlet will help prevent diffusion of the outside air entering the sampling bulb.
1. Sample will be very close to atmospheric pressure after turning the gas supply off.
iii. Inject a known quantity of compound
iv. If necessary, heat the bulb in an oven to vaporize the compounds injected.