A precompression system for a liquid dispensing device is presented, that prevents liquid from being discharged until a predetermined pressure has been built up. The system comprises a pump for drawing liquid through an inlet and discharging it through an outlet, and a precompression valve disposed between the pump and the outlet. The valve allows liquid in the pump to reach the outlet once the predetermined pressure is established, and stops liquid from reaching the outlet once the pressure falls below it. The precompression valve comprises an elastic diaphragm normally closing the valve opening, with a concave surface facing the valve opening and in fluid communication with the pump and a convex surface in fluid communication with atmospheric pressure. The diaphragm may be stretched around a valve seat. Methods of assembling such a precompression system in a dispensing device are also presented.

A flow control valve includes a membrane which has at least one opening for the flow of a fluid and an annular body which has a flow contact surface and at least one flow opening. The flow opening is in flow connection with the at least one opening in the membrane. The membrane is constructed to be bendable in a direction towards the flow contact surface.

A non-return device (10) for use with a waste trap is described. The non-return device comprises a sealing portion (12) having first and second sheet members (14, 16), a device inlet (18), a device outlet (20) and a transition portion (22) providing fluid communication between the device inlet and the sealing portion. The transition portion has a convex section of wall (24).

The valve unit includes: a body having a charging passage; a supply-side joint that connects a supply pipe; and a check valve that is disposed in the gas passage, and that inhibits gas from being discharged from the gas tank to the outside of the body. The check valve includes a check valve seat, a check valve element that comes into contact with or moves away from the check valve seat, and a positioning member that fixes the position of the check valve seat in the charging passage. The body has a fitting hole which is communicated with the charging passage and in which the supply-side joint and the positioning member are fitted. The positioning member is fitted in a second fitting hole so as to fix the position of the check valve seat even when the supply-side joint has not been fitted in a first fitting hole.

A flow limiting device with a back flow prevention mechanism includes a body that has an isolation board and a water-through cavity. The isolation board has a water-through hole connecting to the water-through cavity and a flow limiting device having a flow limiting component and stop ribs which limit the position change of the flow limiting component. The stop ribs are arranged on the inner wall of the water-through cavity at equal intervals. The flow limiting component is set in the water-through cavity. The outer side of the flow limiting component is contacted on the stop ribs. A back flow prevention mechanism comprises, a back flow prevention component which is fixed in the water-through hole and a supporting structure which is set for supporting the back flow prevention component when it expands on the inner wall of the water-through cavity.