Why do the doors on a bus close using the pneumatic system instead of the hydraulic system?


How Pneumatic Systems Work

Pneumatic systems operate in much of the same way as hydraulic systems do. In general, they require an air compressor, which draws atmospheric air in through an intake valve and feeds the air into a receiver tank.

Pressure is then applied to air within the receiver tank. Gases, unlike fluids, can be compressed, making high pressure density easily achievable through the exertion of force. Air is compressed and passed into a network of pipes and valves that direct the flow of air toward an actuator. The actuator will transfer the energy back into mechanical energy in order to initiate motion, as with a hydraulic system.

Why Pneumatic Systems Beat Out Hydraulic Systems

While hydraulic systems may guarantee fewer energy losses during operation, in general, pneumatic systems ensure a lower up-front cost, fewer maintenance demands, greater durability, and a higher degree of mechanical reliability, making them the most cost-effective option in the long-run.

What’s more, compressed air comes with the unique advantage of speed — unlike hydraulic oil, when air is released, it expands at high speed and force, enabling much higher actuation velocities. As such, pneumatic systems offer expanded application possibilities and are the obvious choice for applications requiring high speed and precision.

Pneumatic systems can efficiently facilitate most industrial-scale applications requiring movements such as clamping, positioning, pressing, lifting, sorting, and stacking — such as those seen in manufacturing, assembly, and distribution facilities. Further system modifications can increase the precision with which a pneumatic system operates, enabling applications that require labeling, cutting, crimping, or embossing.

Due to their durability, superior performance, and ability to supply energy to actuators at high speed, pneumatic systems remain among the most reliable choice for powering everything from commuter transit systems and natural gas extraction to agtech devices that can milk a cow autonomously.

Marissa-Anneke Collins Said:

HD truck,bus, and heavy equipment mechanic

To use a hydraulic system, they’d either have to introduce one for the doors or they would have to draw off the power steering.
Don’t know where this supposed hydraulic system came from in your mind, but the functions you’re probably thinking are hydraulic (e.g., kneeling buses) are pneumatic.
Granted, there are wheelchair lifts on some long distance commuter buses which use hydraulics,
but those are a fully self-contained system – they don’t run off of a PTO driven pump like you’d find on a garbage truck, dump truck, etc.

If an air hose fails, it doesn’t leak oil all over the place. I don’t know what your dealings with hydraulic systems are insofar as diagnostics, maintenance, and repair,
but I work on heavy equipment and vocational trucks, and hydraulic systems are not low maintenance, and it’s not uncommon for hoses and o-rings to fail.
If you do get a broken air hose, a simple push in or compression fitting installed in situ will suffice… hydraulic hoses can be crimped, but that requires a crimp tool,
and even the portable ones don’t fit in very tight spaces. If an air hose does fail, air is in infinite supply. The plumbing is simpler,
as all you need are a couple electric-over-pneumatic valves and there is no return to tank – air just gets vented to the atmosphere.
In an emergency, pneumatic operated doors can be quickly disengaged and pushed open manually, as you’re not trying to force fluid back into a reservoir.

It would make no sense for those doors to use hydraulic actuation.

Dan Dykstra said:


air systems have a few intrinsic advantages for a system like this:
1 – they are clean when they eventually leak, and they will leak.
2 – air is compressible so always has some give when the door closes on a passenger – much safer.
This is all beside that fact that large buses have both air brakes and air suspensions and can afford a little more air to operate other systems.

William Taylor said:

heavy equipment mechanic

Many busses already have an engine driven air compressor for the brake system.
Therefore, it is quite easy, less costly, less messy, and less maintenance to use a small volume of air already in the air receiver storage tank to open and close the door.

Contact us

Nanjing Decent Power Technology Co.,Ltd