Lesson 4

1. Read and learn the following words:

damage пошкодження

inlet вхідний отвір

plug стопор

output продуктивність

rotative обертальний

approximately приблизно

piston поршень

lubrication мастило

emergency аварія

valve клапан

auxiliary допоміжний

2. Read and translate the text:

Hydraulic Accumulators and Hydraulic Motors

The purpose of a hydraulic accumulator is to store hydraulic fluid under pressure. It may be used to:

• Dampen hydraulic shocks which may develop when pressure surges occur in hydraulic systems.

• Add to the output of a pump during peak load operation of the system, making it possible to use a pump of much smaller capacity than would otherwise be required.

Absorb the increases in fluid volume caused by increases in temperature. Act as a source of fluid pressure for starting aircraft auxiliary power units (APUs). Assist in emergency operations. Accumulators are divided into types according to the means used to separate the air fluid chambers; these are the diaphragm, bladder, and piston accumulators.

The diaphragm accumulator consists of two hollow, hemispherical metal sections bolted together at the center. One of the halves has a fitting to attach the unit to the hydraulic system; the other half is equipped with an air valve for charging the unit with compressed air or nitrogen. Mounted between the two halves is a synthetic rubber diaphragm that divides the accumulator into two sections. The accumulator is initially charged with air through the air valve to a pressure of approximately 50 percent of the hydraulic system pressure. This initial air charge forces the diaphragm upward against the inner surface of the upper section of the accumulator pressure port, pushing the diaphragm down and further compressing the air in the bottom chamber. Under peak load, the air pressure in the lower chamber forces fluid back into the hydraulic system to maintain operating pressure. Also, if the power pump fails, the compressed air forces a limited amount of pressurized fluid into the system.

The bladder accumulator operates on the same principle and for the same purpose as the diaphragm accumulator but varies in construction. The unit is a one-piece metal sphere with a fluid pressure inlet at the top and an opening at the bottom for inserting the bladder. A large screw-type plug at the bottom of the accumulator is a retainer for the bladder that also seals the unit. A high-pressure air valve is also incorporated in the retainer plug. Fluid enters through the system pressure port. As fluid pressure increases above the initial air charge of the accumulator, it forces the bladder downward against the air charge, filling the upper chamber with fluid pressure.

The piston accumulator serves the same purpose and operates by the same principles as do the diaphragm and bladder accumulators. The unit consists of a cylinder and piston assembly with ports on each end. Fluid pressure from the system enters the left port, forcing the piston down against the initial air charge in the right chamber of the cylinder. A high-pressure air valve is located at the right port for charging the unit. A drilled passage from the fluid side of the piston to the outside of the piston provides lubrication between the cylinder walls and the piston.

Hydraulic motors are installed in hydraulic systems to use hydraulic pressure in obtaining powered rotation. A hydraulic motor does just the opposite of what a power-driven pump does. A pump receives rotative force from an engine or other driving unit and converts it into hydraulic pressure. A hydraulic motor receives hydraulic fluid pressure and converts it into rotative force. The motor has a cylinder block-and-piston assembly in which the bores and pistons are in axial arrangement, the same as in a hydraulic pump. Hydraulic motors can be instantly started, stopped, or reversed under any degree of load; they can be stalled by overload without damage. The direction of rotation of a hydraulic motor can be changed by reversing the flow of fluid into the ports of the motor.