Constant flow valve

A constant flow valve comprising:

• a valve casing having a flow passage including an inlet flow passage and an outlet flow passage, said flow passage having a partition arranged between the inlet flow passage and the outlet passage which defines a curve in the flow passage, a chamber having an axis arranged at an angle to the axis of the inlet flow passage and located between the inlet flow passage and the outlet flow passage, and an opening communicating the inlet flow passage with the chamber and having an inner diameter which is gradually reduced from the downstream side toward the upstream side thereof;
• a cylinder arranged coaxially with the opening, and able to move forward and backward in the direction of the axis thereof and having a sealing surface at the lower end thereof which is pressed against a valve seat of the opening when the cylinder is moved in the forward direction;
• a cap attached to the valve casing and supporting the cylinder;
• a piston type valve plug slidably fitted in the cylinder and having an internal through hole communicating with the opening, the valve plug being arranged coaxially with the opening and being sized to define an orifice between the opening and the end of the valve plug at all slidable positions of the valve plug;
• and
• spring means arranged between the piston type valve plug and the cylinder, to bias the valve plug away from the opening, said spring means including a first spring and a second spring having different spring constants, at least one of said springs being arranged between the cylinder and a spring seat slidably fitted in the cylinder, whereby the valve plug is gradually moved forward and backward in response to a change in the fluid pressure.