Lego pneumatics is a variety of Lego bricks which use air pressure and specialised components to perform various actions using the principles of pneumatics.
History
The LEGO pneumatics components were first introduced as part of the LEGO Technic range in 1984. Since their introduction, LEGO pneumatics have featured in a variety of LEGO Technic and LEGO Education (Formerly DACTA) products.
Generation 1
The first generation of LEGO Pneumatics ran from 1984 through 1988. This generation is characterised by single port pneumatic cylinders and the more complex plumbing including a three port distribution block with a pressure and vacuum outlet port. These pressure and vacuum lines ran to a switch to provide pressure for extension or vacuum for retraction of the pneumatic cylinders. These are often falsely compared to single acting hydraulic cylinders that require gravity to retract. The difference is that these units retract on the application of vacuum rather than gravity.
Generation 2
In 1989, the LEGO pneumatic line was revamped, and a new cylinder and pump piece were introduced. The old cylinders and pumps were discontinued. The chief difference is that the new cylinder had two input valves now, which allowed both pushing and pulling without needing complex circuits involving the distribution block piece. The Generation 2 cylinders also had metal rods so that they more closely resembled real hydraulic cylinders.
Over the years, several new pieces were introduced in this line as well. The new pump was spring based, and could only be operated by hand, which limited pneumatic power to how fast it could be manually pumped. This obviously limited the power of pneumatic circuits. So in 1992, LEGO introduced two new pieces; a small pump and a small cylinder. The small pump did not have a spring on it, and it was designed to be operated by a motor, which would allow for continuously running pneumatic creations. The small pump only appeared in two sets — 8868 Air Tech Claw Rig (1992) and 8049 Tractor with Log Loader (2010) — and a few service packs. A new version of the small pump was released in Lego set 8110 Unimog U400 (2011). At 2L, this pump's stroke is 1/3 longer than the old one's 1.5L, 'L' being the LEGO unit of a stud. This made it much easier to use in studless construction.
In 1997, LEGO introduced the air tank which acts like a battery, storing compressed air so that even more powerful pneumatic circuits can be created. This piece is very popular with the enthusiast community, but many feel that it was underutilised by LEGO, as it only appeared in 3 model sets and a parts pack. This tank was later re-released in a LEGO Education add-on pack, along with a new manometer part.
In 2003, LEGO discontinued the old cylinder and switch parts, and made new "studless" versions to fit in with their transition towards removing studs from Technic sets.
Generation 2.1
In 2015, LEGO decided to make a second version of the pneumatic cylinders and switches with changes that included modifying the ports, giving them a small taper which makes tubing easier to slide on. Many smaller parts, like T-pieces and axle/hose connectors, stayed the same.
Linear Actuator
Beginning 2008, LEGO has released several sets with mechanical linear actuators, which are used for the same purpose as the pneumatic cylinders, but the fact that they can easily be extended to intermediate points means that they approximate hydraulic cylinders more closely.
Lego pneumatics components
The key components of Lego pneumatics are:
Pneumatic pump
Pumps are the primary source of air in a pneumatic circuit. There are three versions of the pump: the old Generation 1 pump, the new Generation 2 pump (both of these are spring-loaded) and the small pump without a spring (designed for use with motors as a compressor). The Generation 1 pump was red, and provided both overpressure and underpressure in each pumping cycle, used for extension and contraction of the cylinders respectively, routed through a distribution block. In contrast, the Generation 2 pump is yellow and only provides overpressure, much like a regular bicycle pump, and has a one-way valve to prevent backflow. It also has a larger contact pad at the top of the pump and contains a relief valve to limit the maximum pressure in the system. Generation 3 pumps are now available in translucent blue.