On a constant displacement pump, how is the output pressure regulated?
It must have some form of regulator or relief valve in the system to relieve the pressure that builds up when the pump moves more fluid that the system can use.
What is the safety feature on the micronic filter assembly?
Relief valves across both elements to prevent over-pressurizing the return if, for any reason, the pressure drop across the elements become excessive.
What is good about the cuno filter?
They are able to be used on the pressure side of the system
On a variable displacement pump, how is the output pressure regulated?
By controlling the amount of fluid that the system will accept
What is the main purpose for pressurizing hydraulic reservior?
To operate at higher altitudes to compensate for the decrease air pressure.
Name some reasons for the quick disconnect coupling.
- Prevents loss of fluid when units are removed
- It can be used interchagably with other systems
- Automatically closes when a line has been disconnected from it
What pump is connected to the standpipe?
Which three things maintain pressure in a hydraulic system? Which part has the lowest pressure?
Thermal relief valve - highest psi
Accumulator - lowest psi
system relief valve - medium psi
Name the three types of fluids
Vegatable based fluids: MIL-H-7644
- Not interchagable
- blue dyed
- castor oil and alcohol made
Mineral based fluids: MIL-H-5606
- Kerosene type petroleum
- Red dyed
Synthetic fluids: Skydrol
- Non-petroleum based/phosphate easter base
- Not compatable with neoprene or Buna-N
- Light purple
What is a one way seal?
The seal will stop the flow of fluid on one direction only
What precaution should be used when removing a pressurized hydraulic reservior cap?
All of the pressurizing air must be released before removing the reservior cap
On a wet style pump, what else is required?
What is a sequence valve used for?
To permit actation only when specific prior events have occured
What is a priority valve used for?
Does not allow flow until a preset pressure is reached. They are opened by a hydraulic pressure rather than by mechanical contact.
How do you remove moisture from a compressor?
Removed from a moisture seperator with final last traces dried out with a desiccant or chemical dryer
What is a moisture seperator?
Collects the water that is in the air on a baffle, holds it until the system shuts down, and blows it overboard through a drain valve. An electrical heater prevents water from freezing, and later a chemical dryer removes any last traces of water.
Wht is the purpose of a relief valve?
Prevents excess pressures from damaging the system through spring tension that can be overcomed to open the valve if pressure is too high
What is the purpose of a check valve?
A one directional flow-control valve
What are some characteristics of the pneumatic system
moisture sperator - 98%
Desiccant - 2%
What are two broad categories of engine driven hydraulic pumps?
What causes chattering of a hydraulic pump?
Name the different seal fluid's base
Natural rubber seal
- vegetable based fluids
- if combined with petroleum based or phosphate easter base, the seals break down
Neoprene seal MIL-H-5606
- mineral base fluids
- Skydrol phosphate ester base
- sythetic fluids
How is packing protected during installation?
Placing tape over the thread
What is the most common used two-way seal?
The o-ring which may be used as either a gasket or a packing or a packing and needs to squeeze or pinch the groove.
What is an unloading valve?
A line between the pump and the selector valve that returns fluid back to the reservior
What is the characteristics of the open center selector valve?
- It's an open center poppet type valve used in an open center hydraulic system
- When in neutral fluid flows straight through the next selector valve and on to the reservior
The instruments used to measure
the viscosity of a liquid are known as
viscometers or viscosimeters