Low Cost Pressure Control Valves - Design

Background

One of my former employers assigned this project to me.  The design criteria was to design a low cost pressure control valve.  The valve must function as a reducing valve as well as an expansion valve.  The reducing valve needed to reduce the incoming upstream pressure to a per determined set downstream pressure.  The expansion valve was to relief any pressure that may build up on the downstream side, acting as a safety feature.  A cost saving of 25% needed to be achieved.  The valve needed to function according to the relevant SABS specification.  Port connections needed to be ½” BSP thread.

Conclusion:

The valve was designed in a single body, featuring the reducing and expansion functions side by side.  The body would be gravity die hand casting using sand cores to generate the cavity.  Design calculations were made with best estimates.  A 3D CAD model was made according to the design calculations and 2D manufacturing drawings were made from the 3D solid model.  All parts were made and drawings checked during the prototype manufacturing stage.  O-rings, seals and springs were bought from suppliers.
Parts were assembled and the valve was fitted to a test bench.  Pressure and flow readings were taken and corrections were made to achieve the desired performance.  Springs and flow passages were changed to obtain the desired performance.

Evaluation and study of the competitor’s products formed a large part of the project.  It would be ideal if the product performs better and costs less than the competitor’s.

During the following design iteration, the reducing valve was separated from the expansion valve.  A threaded port connected the two valves. (see image1)  The pressure-reducing valve also featured a high-pressure outlet port.  This unique feature was patented.  Another benefit was that existing tooling could be used to manufacture the expansion valve body.  This body was made by a forging process and used by another product.  Similarly, old worn-out gravity dies of an existing product was modified and used for casting the pressure reducing valve body.  Existing sand cores were hand-modified to suit the existing design.
Prototype parts were made and assembled.  The assembled prototype was fitted to the test bench and evaluated.  Next followed the accelerated life testing.  The test rig was designed and automated.  Electro-pneumatic techniques were used to test this hydraulic apparatus.

The ½” valve did not quite comply with the SABS specification in some instances.  Another ranges of pressure reducing valves, from 1” pipe diameter upwards, were made, based on the previous design concepts (see images 2 & 3).  The larger valves performed much more superior.  Constant reliable pressure reducing was achieved.  I recommended that there will be a larger cost saving for the community to supply a cluster of homes with one larger pressure control system rather than every home with a pressure control system.

Images:

• 1/2" Low Cost Pressure Control Valve
• 1 1/4" Pressure Reducing Valve
• 2" Pressure Reducing Valve