The present invention relates to valve apparatus for regulating flow. The apparatus comprises a valve housing having a bore. A piston member (7) is movable within the bore, a first spring member biasing the piston member in a first direction within the bore. A first rod (12) extends through the piston member, the first rod having an end (13) for engaging a second spring member (14) provided between the end (13) and a spring seat (8). The piston member (7) and spring seat define a chamber (9) which houses the second spring member (14) and into which the first rod is slidably received. Further, a second rod extends from the spring seat and is coupled to valve member seat. A damping means is provided to damp the movement of the chamber (9) within the bore.

A damping valve includes a damping valve body with an annular groove which has a base and which is limited by an inner valve seat surface and an outer valve seat surface for at least one valve disk. The base of the annular groove has a maximum distance from the valve seat surface along a circumferential area and has a minimum axial distance from the valve seat surface in another circumferential area.

A damping valve includes a damping valve body with an annular groove which has a base and which is limited by an inner valve seat surface and an outer valve seat surface for at least one valve disk. The base of the annular groove has a maximum distance from the valve seat surface along a circumferential area and has a minimum axial distance from the valve seat surface in another circumferential area.

A valve assembly includes a piston housing inside a flow duct between an inlet and an outlet so as to form an annular flow passage between the flow duct and the piston housing. The piston housing is axially aligned with a center axis of the flow duct. A piston is inside the piston housing and is configured to extend downstream of the piston housing in a closed position. A spring biases the piston to the open position. A fluid chamber is between the piston and an upstream end of the piston housing. A control opening extends through the upstream end of the piston housing and fluidically communicates with the flow duct and the fluid chamber. A control piston and a control spring are inside the piston housing. The control spring biases the control piston toward a first position that obstructs the control opening.

An actuating system comprising a hydraulic actuator provided with a cylindrical cavity containing a piston configured to slide within the cylindrical cavity and a rod. The piston separates the cylindrical cavity into a first actuating chamber and a second actuating chamber. A first servo valve comprises a sheath including a first slider configured to slide within a cavity of the sheath on the basis of command signals from a command system. The cavity of the sheath comprises a first command chamber and a second command chamber on either side of the first slider. The first actuating chamber is fluidically connected to the first command chamber, and the second actuating chamber is fluidically connected to the second command chamber.

An actuating system comprising a hydraulic actuator provided with a cylindrical cavity containing a piston configured to slide within the cylindrical cavity and a rod. The piston separates the cylindrical cavity into a first actuating chamber and a second actuating chamber. A first servo valve comprises a sheath including a first slider configured to slide within a cavity of the sheath on the basis of command signals from a command system. The cavity of the sheath comprises a first command chamber and a second command chamber on either side of the first slider. The first actuating chamber is fluidically connected to the first command chamber, and the second actuating chamber is fluidically connected to the second command chamber.

Embodiments of air admittance valve assembly and plumbing system incorporating the same are provided herein. In some embodiments, a valve assembly comprising a housing, a first valve comprising a first valve sealing member and a first valve seat, and a second valve comprising a second valve sealing member and a second valve seat, and a pipe, an inlet, an outlet, a first zone, a second zone, a third zone, the first and second valve sealing member is closed by gravity and open based upon the pressure differential between the first zone, second zone and third zone.

A reciprocating compressor comprising a cylinder and a piston dividing the cavity in the cylinder into a first and a second chamber being connected through respective suction valve systems and discharge valve systems to a suction duct and a discharge duct. The suction and discharge valve systems each including a housing defining a valve chamber and a valve body, whereby the compressor is further provided with a vessel defining a volume in fluid connection with a valve chamber of one of the discharge valve systems by a conduit.

A reciprocating compressor comprising a cylinder and a piston dividing the cavity in the cylinder into a first and a second chamber being connected through respective suction valve systems and discharge valve systems to a suction duct and a discharge duct. The suction and discharge valve systems each including a housing defining a valve chamber and a valve body, whereby the compressor is further provided with a vessel defining a volume in fluid connection with a valve chamber of one of the discharge valve systems by a conduit.

The invention relates to a compressor unit (200) for a refrigeration system using a refrigerant. The compressor (200) unit includes a centrifugal compressor (201) for compressing the refrigerant, wherein the compressor (201) has a discharge outlet (204) for discharging the compressed refrigerant, and a check valve (1; 100; 301a). An inlet (83) of the check valve (1; 100; 301a) is in fluid connection with the discharge outlet (204) of the compressor (201). In order to provide a more reliable and more quite compressor unit (200), the check valve (1; 100; 301a) is a nozzle check valve including a damping mechanism (41, 50; 50, 141), wherein a closing parameter of the check valve (1; 100; 301a) is between 50 s/m.sup.2 and 2000 s/m.sup.2, wherein the closing parameter is a closing time of the check valve (1; 100; 301a) divided by a port area of the check valve (1; 100; 301a).