The DMT slow vent valve is on the pannel of the DMT Control Unit. It is used to flush the pressure slowly after the B-reading, in order to take the C-readings.
The knob is turned counterclockwise to enable the flush and clockwise to stop the flush. The valve does not regulate the intensity of the flow, it is either in the open or closed position.
 
Important Note: After venting with this (grey) slow vent valve, the flush must be stopped by turning the knob clockwise. If the flush is not stopped, the pressure will leak through this valve and all the subsequent DMT readings will be mistaken.
 
Weight: 0.12kg
Dimensions: 25mm x 70mm x 50mm