EMCO Multi-Stage Depressurizing Unit for Gas. The gas passes each stage at sonic or critical velocity. When the pressure is reduced so is the density of the gas or steam. In order to maintain a constant velocity the cross sectional area is increased after each stage. The calculation is based on R.W. Miller and Ward-smith. Each of the pressure reducing stages are connected and supplied as a unit EMCO single hole multi stage depressurizing units (SDP-G) are used to reduce the pressure in a number of stages to a desired pressure. EMCO multi hole multi stage depressurizing units (MDP-G) are used to reduce the pressure in a number of stages to a desired pressure and to secure as low noise development as possible.