Pressure Equalisation

Pressure equalisation recovers work and gas by connecting a bed that is finishing a high-pressure step to a bed that is at low pressure, so gas flows from one to the other until their pressures approach each other. It improves recovery and reduces compression duty, and is a standard feature of multi-bed PSA cycles.

There is no dedicated "equalisation" object — you build it from a valve on each bed connected together. The valve turns the flow into a pressure-driven exchange: gas moves from the higher-pressure endpoint to the lower-pressure one at a rate set by the valve coefficient.

Setting it up

You need two steps, running for the same duration (they represent the two beds equalising at the same time):

Equalisation-down step (the bed releasing gas):

On the end that connects to the other bed, set the boundary to Flow, direction Outlet, and add a stream with Boundary Device Type = Valve.
Enter a Valve Flow Coefficient (Cv) and a target pressure.
Set the opposite end to Closed.

Equalisation-up step (the bed receiving gas):

Mirror the setup: a Valve stream, direction Inlet, on the connecting end.
Set the opposite end to Closed.

Connect them: on the Cycle Design → Interacting Steps tab, connect the two valve endpoints. Once connected, each valve uses the other bed's pressure as its driving pressure, so gas flows down the pressure gradient between them.

Tuning

The valve coefficient (Cv) controls how quickly the beds equalise. A small Cv throttles the exchange so the pressures approach gently over the step; a large Cv equalises almost immediately. Choose Cv together with the step time so the beds reach the intended intermediate pressure by the end of the step.
For multiple equalisation stages, repeat the pattern with additional step pairs, each equalising to a successively lower pressure level.

Remember the coupling is lagged by one cycle: the two beds converge on the true shared equalisation pressure as the simulation approaches cyclic steady state, not on the very first cycle.