Feeding a low pressure gas into a higher pressure reactor

Solvent A reacts with gas B. The reaction is catalyzed by C, which is soluble in A. The reaction is inverse 1st-order in B, so high pressures of B slow the reaction down. The reaction is performed at a very high temperature–so high that a high pressure of an inert gas, D, is added to keep A a liquid. Without D, most of A is a gas, C precipitates out, and results are irregular. The reaction is set up by adding A and C to the reactor, which is purged with B (~1 atm), and pressurized (~8 atm total) with D.

Here’s the question. How does one replenish gas B as it is consumed in the reactor? Not knowing how the innards of gas regulators work, I was wondering if there’s just a simple way to set an inlet of B at 9 atm*. As the 1 atm of B is slowly consumed, the total pressure (B + D) will be brought back up to 9 atm, but with the partial pressure of B remaining at 1 atm. This works so long as there is no backflow of D to contaminate the source of B.

*Afterthought: The pressure will need to be set higher since the internal pressure of the reactor will obviously rise as T goes up.
**Since this isn’t actually my work, I just made up the numbers.