OPERATION AND MAINTENANCE MANUAL
01-2016
4
2 DESIGN
2.1 DESCRIPTION OF THE VALVE DESIGN
The Type BA antipollution check valves supplied by F.A. JAFAR S.A. are flanged valves. The
antipollution check valve is designed with a cast iron tubular body, a valve cover and two poppet valve
units, which form the valve closing components, and a membrane drain valve. The two closing components
are poppets with rubber seals. Each poppet is seated on a spring and within a guide that enables
reciprocating action. The poppet and its guide are made of brass. The poppet seal seat is located within the
guide. The valve body is divided into three chambers separated by the two poppet assemblies. Both poppets
are located on the valve outlet end which facilitates movement of the spring-supported poppet away from its
seat to open the valve under the incoming water pressure. If the water flow ceases, the spring moves the
poppet automatically to the seat which closes the valve and prevents backflow. Under the valve body cover
is a membrane valve, located within the centre line and transverse to the direction of water flow. The
membrane valve is a disk installed on a metal spindle, one end of which is within the valve cover bush and
the other is within the drain port seat, located at the valve body bottom. The chamber over the membrane
disk is open to the valve inlet chamber. The chamber under the membrane disk is the central zone between
the inlet and the outlet ends and separated by the two poppet closing components. Hence the membrane
valve is a pilot which seals off the bottom drain port when the flow comes into the valve and opens the drain
port when the flow is gone. The operating parameters of each mushroom closure assembly make the drain
port close when the medium pressure is present in the antipollution valve, followed by opening of the inlet
poppet and then opening the outlet poppet. If the pressure drops, first the inlet poppet is closed, followed by
the outlet poppet. When the inlet pressure drops to a pressure differential of 0.14 bar (0.014 MPa) between
the inlet chamber and the middle chamber, the membrane valve spring opens the drain port seat to evacuate
the middle chamber. This action applies only when the supply pressure drops. During the normal operating
cycle, the drain valve should not open.
The antipollution valve body has three tapped inspection holes, each for one zone of the valve. The Type BA
antipollution valves installed in horizontal pipes shall have the inspection holes pointing upwards. The
inspection holes are sealed with threaded plugs and facilitate control by sampling.
All inner and outer cast-iron surfaces of the valve are protected against corrosion with epoxy powder
coating.
