When performing tests that require more precision and a validation procedure it is usually necessary to purchase a packaged system. There are a number of good manufacturers of leak and flow testers around, the latest I have used is Cincinnati Test Systems or CTS. Not only do they make excellent equipment with great documentation and application assistance, they also make calibrated orifices and are only about 250 miles away!
Purchased systems such as this have a lot in common. There is an onboard controller with I/O connections, generally 24vdc. There are various communication ports for exchanging information with a PLC or computer as well as a separate programming port and usually a printer port also. These ports may be assignable as to communication protocols. Ethernet/IP, RS232 or open protocols such as DeviceNet or Profibus are common. The RS232 or Ethernet ports generally transmit a configurable string containing test data, time/date and selected program information. This allows the parsing of the string(s) for the data that the user requires for archiving and display.
Fixturing the tested device usually involves some kind of rubber seal. This may be a solid surface that the product is pressed against or an inflateable bladder that is inserted into a round hole. Regardless of the type of sealing the process usually involves movement of the part or tooling (or both) which brings the aspect of safety, i.e. light curtains or physical guarding into the picture.
The interface generally allows the test parameters to by set by program number. Fill time, stabilize time, test time and pass or fail criteria are settable within the interface. Alternatively, these can be externally controlled by means of I/O. A special mode for calibration allows the user to place a calibrated orifice into the flow circuit to test to a known standard. This can be automated for a periodic check.
As I mentioned before, leak, flow and pressure testing can be very simple or involve rigorous validation and calibration procedures. Most of the leak testing work I have done has been for the automotive, pharmaceutical or packaging industries, but it is common in many other manufacturing areas also.