Graph shows depth of seal remaining after six test applications of suction induced by the stated fl ow held for 15 seconds. (Note: Seal not replenished between tests)
Operation. Should there be a tendency for siphonage (suction), the air inside the trap is drawn out and the valve simultaneously rises, thus neutralising the pressure. As soon as the action is fi nished, the valve closes air and watertight (see also BRE Report 1911).