Gas Networks Notes

The Ideal Gas Law

The ideal gas law allows us to model gas pressure at "normal" temperatures and pressures [Ref]: Where:

is pressure in atmospheres.
is the number of gas particles in moles.
is the universal gas constant - 0.0821 atm L / mol K.
is the temperature in Kelvins.
is the volume in litres.

This tells us that if volume is constant, the more gas that is pushed into a network, the higher the pressure.

Hooke's Law And Sping Constant

The force exerted by a spring can be described using Hooke's law: Where:

is the restoritative force exerted by the spring under extension or compression in newtons.
is the spring constant.
is the extension or compression in meters.

Relating Force To Pressure And Vice Versa

Force is related to pressure as follows: or...

A Basic Govenor Valve

The Fisher guide gives a nice summary of a governor's pupose:

The primary function of any gas regulator is to match the flow of the fas through the regulator to the demand for gas placed upon the system. At the same time, the regulator must maintain the system pressure within certain acceptable limits...

...If the load flow decreases, the regulator flow must decrease also. Otherwise, the regulator would put too much gas ... into the system and the pressure would tend to increase. On the other hand, if the load flow increases, the the regulator must increase also in order to keep ... [pressure] from decreasing due to a shortage of gas in the [network]... Theoretically, for force excerted on the govenor's pilot spring can be related to the gas outlet pressure using the above equations.

The Fisher's guide also gives some useful terminology that is important to know:

Setpoint

The constant pressure desired is represented by the setpoint. but no regulator is ideal ... The setpoint is determined by the initial compressure of the regulator spring ...

Droop

Droops, proportional band, and offset are terms used to describe the phenomenon of pressure dropping below setpoint as flow increases. Droop is the amount of deviation from setpoint at a given flow, epxressed as a percentage of setpoint...

Accuracy

The accuracy of a regulator is determined by the amount of flow it can pass for a given amount of droop. The closer the regulator is to the idea regulator curve (setpoint), the more accurate it is.

Lockup

Lockup is the pressure aboe setpoint that is required to shut the regulator off tight...  