Back pressure valves are well known in the art and are generally employed in fluid exhaust lines. A back pressure valve is designed to maintain a given pressure drop across it as a fluid flows past it. Various designs of back pressure valves are available, including a valve that comprises a flexible diaphragm resiliently urged against a valve seat.
The basic principle of diaphragm-based back pressure valves is to provide an outlet member with an end or sealing face. A flexible diaphragm is mounted spaced slightly from the sealing face surrounding the outlet member. An adjustable spring is provided for adjusting a load on the diaphragm, pressing the diaphragm against the sealing face. An inlet chamber is usually annular and surrounds the outlet member. Thus, for fluid to flow from the inlet chamber to the outlet member, the fluid pressure must be high enough to displace the diaphragm away from the sealing face, and then fluid flows from the annular inlet chamber across the sealing face to an outlet chamber. If the fluid pressure is too low, then the load or pressure set by the spring maintains the diaphragm pressed against the sealing face.
There are a number of problems associated with conventional back pressure valves. Firstly, conventional back pressure valves tend to be large and cumbersome. Secondly, conventional back pressure valves only serve to relieve pressure, and thus do not accurately sense or control the pressure. Accordingly, separate measuring and controlling devices must be provided to work in conjunction with the back pressure valve to maintain a stable pressure. This necessitates additional lines and/or hoses, thus increasing the size and complexity of the system. Additionally, since conventional systems have two separate devices for the relief and control of fluid pressures, the systems tend to be slow acting, and possess inadequate dynamic controllability. In conventional back pressure valves, the area of the diaphragm subject to fluid pressure is larger in the open state than in the closed state, as in the closed state only an outlet annular area is subject to fluid pressure. This again affects the performance of the valve.
There remains a need for a back pressure valve with a pressure controlling device that can offer rapid dynamic fluid pressure control, as well as precise and accurate control of fluid pressures in a line.