Pneumatic Control Systems

Welcome to our new technology blog about past, present and exciting new technologies.

First up, we look at Pneumatic Control Systems.

Put simply, pneumatics is a branch of engineering that makes use of gas or pressurized air. In engineering, pneumatic control systems can be an effective and economical choice for those designing commercial buildings, yet it isn’t used as much as it once was.

How Do Pneumatic Controls Work?

A pneumatic control system uses compressed air as a method of control for HVAC systems. Compressed air is carried via copper and plastic tubes from a controller to a control device, usually a damper or valve actuator. This control method relies on sensors and thermostats that bleed or retain the line pressure from the sensor to the control device and the actuator. Each senor responds to changes in temperature, humidity, and static pressure as examples, to provide feedback in a control loop to open or close the actuator to meet the control set point. The actuators contain diaphragms and spring to function in sequence with the control signal. This system uses the compressed air as the communication method. Each thermostat in a building with a pneumatic control system has one or more air lines connected to it from the main source of compressed air and to some type of final device such as a valve.

Reasons to use pneumatics

Actuators

Pneumatic actuators, the air-powered "motors" which control valves and dampers, remain the most reliable, durable, and economical actuators available. They require essentially no maintenance except for inspection and adjustment of the mechanical linkages. It is easy to select actuators which fail in the desired position upon loss of electric power (and thus pneumatic air pressure). Pneumatic actuators, of all sizes, cost much less than corresponding electric/electronic actuators

Modular control components

The complete pneumatic control system "brains" are distributed throughout the building using numerous pneumatic building blocks such as thermostats, receiver controllers, and pneumatic relays. Virtually any control strategy can be implemented by a custom-designed pneumatic control system. Pneumatics can provide excellent control performance and can maintain setpoints accurately.

Limitations of pneumatics

By its own design, the method of using pneumatics is not overly complicated, however there is a tendency of modern building managers to overlook the need for pneumatic maintenance, or to mistakenly believe that the same person who sweeps the floors can maintain the controls. Pneumatics require two important types of maintenance. The first is to ensure that the pneumatic air supply is clean, reliable, and dry at all times. The second is to carry out a program of routine and preventative maintenance under which all control components are inspected and, if necessary, adjusted every couple of years or so. (Left unattended, pneumatic controllers and thermostats may eventually drift away from setpoint). For many commercial buildings, the best way to maintain pneumatic controls systems is to have a service contract with an outside company

Whilst the technology continues to be used successfully, operational systems are functioning with components that are 40 to 50 years old and sometimes given their age, these systems are deemed to be un-serviceable and there are many cases where pneumatic systems have been pulled out and replaced because of perceived poor performance.

Pneumatic controls are generally replaced by more modern DDC (Direct Digital Controls) based systems partly because they are seen to be a more antiquated and less effective method of control, yet a lot of the issues with pneumatics stems from poor maintenance rather with the ability of the technology.