Line A pt 2. Flashcards
What are hydraulic jacks used for apposed to being used for lifting great heights?
They are used for lifting heavy loads mainly.
How many pistons are in hydraulic jacks?
Two:
A smaller pumping piston
A larger lifting piston.
What is the relation of the small pump piston and large lifting piston in a hydraulic jack?
The small pump piston forces oil against the larger lifting piston.
How is the mechanical advance determined in a hydraulic jack?
The mechanical advance is determined by the ratio of the small pump piston and larger lifting piston.
For some hydraulic jacks, how can the total length of the jack be adjusted?
By using an adjustable screw head.
How do some hydraulic jacks open and close the valves at the base of the body?
Using an adjustable handle made from short length steel tubing and a pair of notches at the end.
How do you lift a load with a hydraulic jack?
Close the valve on the jack, insert the handle into the pump, and move the handle up and down.
How do you lower a load supported by a hydraulic jack?
Turn the handle at the base of the jack counter clockwise.
Why should the valve be opened slowly when a hydraulic jack is supporting a load?
By opening the valve slowly the supported load is lowered slowly.
When should one rely on a hydraulic jack to hold a load for an extended amount of time.
Never. Due to an often small internal leakage of fluid, the load will eventually and gradually creep down.
When does the capacity of a mobile crane decrease?
When you extend or lower the boom.
The boom is the arm of the crane.
Can a load be pulled sideways by a crane?
No. Always position the hook of a crane directly above the load.
When should a safety check of a mobile crane be done?
Prior to operating the machine.
At what centered measurement is the capacity of a lift truck usually determined?
At 24” from the heel of the forks.
Where should the capacity of a lift truck be displayed?
On a name plate attached to the machine.
How many pulleys can be grouped together to form a block?
Two or more pulleys.
Pulleys are grouped together in housings or frames, creating what is known as what?
A block.
What is a tackle?
A tackle is the rope or cable that is threaded through the blocks.
Describe a fixed block.
This block does not move and is anchored to a secure point, such as a ceiling, a beam, or a wall.
Describe a travelling block.
This block is attached to the load. As the rope is pulled, this block moves along with the load.
Why is it important to know the lifting capacity of a load?
Because the load to be lifted could possibly be higher than the breaking strength of the rope.
How can the increased lifting capacity of a manual lifting device be calculated?
By counting the number of rope segments coming out of the travelling block.
For example, if the travelling block has 4 rope segments coming out of it and is supporting the load, the mechanical advantage (MA) is 4. This means the input force required to lift the load is reduced by a factor of 4. If you need to lift a 400-pound load, you would only need to exert a force of 100 pounds.
What kind of braking and safety system does a block and tackle have?
None.
A block and tackle cannot support a load until the lifting device is _______.
Anchored.