Metal diaphragm valve
A metal diaphragm valve includes a body with a valve seat provided to a valve chamber communicating a primary flow path and a secondary flow path, a metal diaphragm having a center portion disposed above the valve chamber, the center portion vertically moving to make contact with the valve seat, and a stem provided above the metal diaphragm so as to be able to freely ascend and descend to cause the center portion of the metal diaphragm to move downward. A flow-path restriction part is provided to a part of the secondary flow path. The metal diaphragm valve is quite suitable as a valve for ALD process, the valve favorably reduces fluctuations of a Cv value due to deformation of a resin-made valve seat with time even after the valve is opened and closed at a level of ten million times while a fluid at high temperatures is flowing.
1. A metal diaphragm valve comprising:
a body having a single primary flow path and a single secondary flow path formed therein;
an annular valve chamber formed between a ring-shaped valve seat and an outer-peripheral seal part and communicating with the primary flow path and the secondary flow path, wherein the primary flow path opens to the valve chamber through a center of the valve seat, and a chamber side portion of the secondary flow path forms a short cylindrical space and is directly connected to a bottom surface of the valve chamber;
the valve seat is flexibly deformable and is disposed at an opening of the primary flow path;
a metal diaphragm having a center portion disposed above the valve chamber, the center portion configured to move in a vertical direction and so as to repeatedly press the valve seat, the metal diaphragm includes an outer edge part, the outer edge part configuring the outer-peripheral seal part;
a stem disposed above the metal diaphragm and configured so as to be able to freely ascend and descend to cause the center portion of the metal diaphragm to move downward;
a flow-path restriction part directly connected to the chamber side portion of the secondary flow path; and
a diameter-enlarged exit flow path directly connected to the flow-path restriction part,
wherein a first restriction rate is defined as a diameter of the flow-path restriction part divided by a diameter of the chamber side portion of the secondary flow path and is in a range equal to or larger than 0.58 and smaller than 1,
wherein a diameter of the diameter-enlarged exit flow path is larger than that of the chamber side portion of the secondary flow path,
wherein a second restriction rate is defined as the diameter of the flow-path restriction part divided by the diameter of the diameter-enlarged exit flow path and is in a range equal to or larger than 0.5 and equal to or smaller than 0.86,
wherein a crushing amount from a reference height of the valve seat is in a range larger than 0 mm and equal to or smaller than 0.1 mm, and
thereby providing an effect that the flow-path restriction part is provided so that fluctuations of a Cv value of the valve between a start of use of the valve and after opening and closing fifteen million times while a fluid at high temperatures is flowing are 7% or less.
2. The metal diaphragm valve according to claim 1 , further comprising:
an actuator mounted on the body;
a spring incorporated into the actuator and configured to cause the stem to descend;
a piston incorporated into the actuator and configured to ascend in response to a supply of compressed air; and
an adjustment screw configured to adjust an ascending amount of the piston by screwing the adjustment screw so as to adjust a Cv value of the valve.