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53 Cards in this Set
- Front
- Back
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What is Pascal's law? |
Pressure applied to a confined liquid is transmitted equally and undiminished in all directions at right angles to all surfaces. |
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Why do we need round pressure vessels? |
Pressure will concentrate at the corners and have a compounding effect. |
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What is the difference between laminar flow and turbulent flow. |
Laminar is linear and turbulent flow varies in velocity and direction. |
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How is pressure developed? |
A resistance to flow. |
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What is pressure loss? |
The pressure created by the resistance of system components. |
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Explain the difference between mass and weight. |
Mass is how much material is in the object. Weight is the force of gravity acting on a mass. |
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What is the function of pressure used for in a hydraulic system? |
It is used to generate force. |
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How do you find annular area of a hydraulic cylinder? |
Subtract the area of the rod From the area of the piston. |
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When increasing the diameter of a conductor by 2 what happens to the velocity of the fluid? |
Velocity decreases by 4 |
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What is the hydraulic equivalent to an electrical relay? |
Pilot operated directional control valve. |
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What are the principals of a series hydraulic circuit? |
There is only one path of flow and and both actuators operate at the same time. |
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What are the principals of a parallel hydraulic circuit? |
There is more than one path to flow and the cylinder with the least resistance moves first. |
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What do we call the pressure created by the weight of the fluid? |
Head pressure. |
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Define atmospheric pressure. |
The pressure created by the weight of the air. |
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What is the bourdon tube gauge? |
A gauge that uses pressure acting on a tube that is trying to straighten out cause the needle linkage to move. |
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What is the difference between PSIA and PSIG gauges? |
PSIA will measure 14.7 at sea level. PSIG will measure 0. |
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What is the base unit of measure for pressure in metric? |
Pascal |
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What am I measuring when I use a mercury manometer? |
A low pressure, either positive or negative. |
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What causes liquid flow? |
A difference in pressure. |
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What component is responsible for liquid flow in a hydraulic system? |
The pump. |
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What is velocity measured in in the imperial system? |
Feet per second. |
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What determines actuator cycle time? |
Hydraulic pump flow rate and actuator volume. |
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What are some ways to Change actuator speed? |
1. Pump displacement. 2. Pump speed. 3. Flow control valve. 4. Directional control that is designed to feather. |
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Explain a differential cylinder. |
Force and speed generated are different due to different piston surface areas because of actuator rod. |
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What needs to be done before actuator cycle time tests are performed? |
1. Ensure no load on device. 2. Check mechanical linkage. 3. Isolate from mech. |
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What are the four functions of hydraulic oil? |
Transmit power, cool, seal and lubricate. |
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What are some qualities we look for in hydraulic oil? |
Prevent rust, formation of sludge, varnish and gum, suppress foaming, retain stability, maintain viscosity, prevent corrosion and pitting, let water settle out (unless water-based), and be compatible with seals and gaskets |
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What will be seen in a hydraulic system if oil viscosity is too high? |
Power required to drive system will be higher, high operating temps., greater pressure drops throughout the system, possible sluggish operation, and greater retention of air |
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What will be seen in a hydraulic system if oil viscosity is too low? |
Increased internal leakage (oil temp will rise), actuator speeds will be reduced, excessive component wear (reduced film strength) |
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What are three ways to measure oil viscosity? |
Absolute, kinematic and relative |
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When measuring relative viscosity, what unit of time do we use? |
Saybolt Universal seconds |
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If I have oil with a high viscosity index number, what properties will I see in that oil? |
The oil viscosity changes very little over a wide temp range |
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What is the oils pour Point referring to? |
The lowest temp the oil will flow |
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What does full film lubrication mean? |
When the clearance between two parts is sufficient to allow the film of oil to completely separate them |
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What is added to oil to Aid in boundary lubrication properties? |
Anti-wear and extreme pressure additives |
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What are three items that contribute to oil oxidization? |
The amount of air the oil is exposed to, temp of the oil, chemical makeup of the oil |
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What is an indicator of different oil viscosities in a reservoir? |
It will appear layered |
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What is the ideal size for a hydraulic Reservoir? |
Two to three times the pump output |
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What are the three functions of a hydraulic Reservoir? |
Store of the oil cool and allow for air and contaminants to separate from the oil |
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In a vented Reservoir what pressure is acting on the surface of the oil? |
14.7 PSIA or atmospheric pressure |
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What is the main reason for a pressurized Reservoir? |
To keep the inlet line to the pump flooded constantly |
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Why is the return line in a tank cut at a 45 degree angle? |
To direct the oil away from the inlet to allow Cooling, deaeration, and sedimentation. |
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How many microns are in a meter? |
1 million |
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What are three types of contamination found in a hydraulic system? |
Ingress, built-in, and internally generated |
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How is sieve size measured? |
Openings per linear inch |
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Explain the differences between a positive and non positive displacement pump. |
An non-positive positive pump has hydraulically connected Inlet and Outlet, is used to create high flow but low pressure, and have the outlet blocked off without damaging the pump. A positive pump is mechanically sealed between Inlet and Outlet; it can develop high flow as well as high pressure and can't have the outlet blocked without causing pump damage |
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How do we calculate pump flow rate? |
Take the rated pump speed and multiply by Pump displacement for one revolution. Then divide 231 inches cubed for US gallons or 1,000 cm cubed for liters |
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What is the definition of mechanical efficiency in regards to a hydraulic pump? |
How much power is required to overcome the internal friction of the pump |
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What is the definition of volumetric efficiency in regards to a hydraulic pump? |
A comparison between the theoretical delivery and actual delivery of a pump at rated pressure and RPM |
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What are the two basic types of gear pumps used? |
Internal gear (Crescent gear) or external gear |
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Why is a gear pump considered unbalanced? |
High pressure acts on the outlet side of the pump, Low Pressure Works on the inlet side of the pump causing the gears to be forced towards the inlet side of the pump |
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What is the purpose of the pressure plates in an external gear pump? |
They create a sealing action between the Gear face and pressure plate by way of high pressure oil acting on the backside of the pressure plate |
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If the inlet on a pump is twice the diameter of the outlet, what will happen to the outlet oils velocity? |
The velocity will increase by four times |
