Hydraulic Pumps - Hydraulics - Airframes & Aircraft Systems #7

Summary

This lesson explores various types of pumps integral to aircraft hydraulic systems, including hand-operated, engine-driven, and backup options like pneumatic, ram air turbine, and hydraulic power transfer units. It details the functioning of constant delivery fixed volume pumps and constant pressure variable volume pumps, highlighting their mechanisms and components. The video also addresses safety measures like motorized firewall shutoff valves and the importance of system redundancy for hydraulic power in aircraft.

Takeaways

• 🛫 **Types of Pumps in Aircraft**: The lesson discusses various pumps used in aircraft, including hand-operated, engine-driven, EDP electric motor-driven, pneumatically operated, and hydraulically operated pumps.
• 🔧 **Pump Functions**: Pumps are crucial for drawing oil from the reservoir and delivering fluid to the aircraft's hydraulic systems.
• 🔁 **Backup Systems**: Pneumatically operated pumps, RAT, and PTU are used as backup supplies to ensure hydraulic system redundancy in case of engine or EDP failure.
• ✈️ **Ram Air Turbine**: The ram air turbine is used as a backup to operate primary flight controls and brakes.
• 🤚 **Hand Pumps**: In light aircraft, hand pumps may be the sole source of hydraulic power, featuring double-acting mechanisms and non-return valves.
• 🔧 **Powered Pumps**: Larger aircraft use powered pumps for ground servicing without engine operation, including constant delivery fixed volume and constant pressure variable volume types.
• 🔄 **Constant Delivery Pumps**: These pumps provide a fixed volume of fluid at a relatively low pressure and require an automatic cutout valve and accumulator for proper operation.
• 💧 **Variable Volume Pumps**: Constant pressure variable volume pumps adjust fluid volume and pressure, with components like a kidney plate and rotating cylinder block.
• 🔄 **Pump Operation**: The operation of pumps, including the movement of pistons and control of swashplate angles, is detailed to explain how they maintain pressure and fluid flow.
• 🛑 **Safety Features**: Aircraft hydraulic systems include safety features like motorized firewall shutoff valves to isolate pumps in case of engine fire or internal leaks.

Q & A

What is the primary function of pumps in aircraft hydraulic systems?

Pumps in aircraft hydraulic systems are used to draw oil from the reservoir and deliver a supply of fluid to the system.

What are the different types of pumps mentioned in the script?

The script mentions hand-operated, engine-driven, EDP electric motor-driven, pneumatically operated, ram air turbine driven, and hydraulically operated pumps using a power transfer unit (PTU).

Why are backup pumps important in aircraft hydraulic systems?

Backup pumps like the pneumatically operated pump, RAT, and PTU provide hydraulic system redundancy in the event of engine or EDP failure, ensuring the primary flight controls and brakes can still function.

What is the typical use of a hand pump in an aircraft?

In light aircraft, a hand pump may be the only source of hydraulic power. In larger aircraft, it allows ground servicing without engine running, enabling pressure testing of lines and operation of cargo doors.

How does a double-acting hand pump work?

A double-acting hand pump delivers oil on both strokes. It has a piston assembly with a transfer valve and non-return valves, allowing fluid to flow from below to above the piston during one stroke and from above the piston during the other stroke.

What are the two types of powered pumps commonly used in aircraft?

The two types of powered pumps are the constant delivery fixed volume type and the constant pressure variable volume type.

How does a spur gear displacement pump operate?

A spur gear displacement pump operates by having one gear driven by a power source, which in turn drives another gear. Fluid is carried around in the spaces between the teeth from the inlet to the outlet side of the pump.

What is the purpose of an automatic cutout valve (ACOV) in a hydraulic system?

An automatic cutout valve (ACOV) is used to return fluid to the reservoir when the actuators have reached the end of their travel and the system is not operating, preventing constant cycling of the ACOV.

How does a constant pressure variable volume pump control its output?

A constant pressure variable volume pump controls its output by varying the angle of the swashplate, which in turn changes the piston stroke. The control piston moves based on system pressure, adjusting the swashplate angle to maintain pressure.

What is the function of the case drain fluid in a hydraulic pump?

The case drain fluid cools the pump before it is returned to the reservoir. It is also an indicator of the pump's condition, as any issues with the pump can be reflected in the condition of the case drain filters.

Why is a motorized firewall shutoff valve necessary in engine-driven hydraulic pumps?

A motorized firewall shutoff valve is necessary to isolate the pump from the flammable hydraulic fluid supply in the event of an engine fire or an internal pump leak, preventing further damage to the pump due to lack of cooling or lubricating fluid.