Frequent Terms & Definitions

Ram = Piston = Plunger

The plunger is the part of the jack that rises out of the housing (cylinder body). The plunger is also referred to as a “Piston” or “Ram”.

Stroke

The “stroke” means how high the jack is able to lift from the retracted position. The “stroke” it is the height difference between a retracted and extended jack.

Flow Rate

The flow rate is the amount of oil, the pump delivers to the cylinder (… for hand pumps with one hand stroke, … for electric and air pumps per minute). The larger the flow rate, the faster the cylinder will rise. Some pumps are equipped with double speed: With the cylinder unloaded, the pump delivers a high volume of oil for fast cylinder speed. Once the load is engaged, the pump automatically switches to the slower high pressure lifting stage.

How many hand strokes are required for a hand pump to raise a cylinder?
Hand strokes = Cylinder oil capacity / Oil volume per stroke.

Low-cycle vs. High-cycle

General purpose cylinders are limited to the number of raise and retract cycles they can sustain before maintenance considerations become an important factor.

Low-cycle: Infrequent use of cylinder. Mainly used in construction and maintenance.

High-cycle: Continuous up and down movement of plunger/piston. Used in production. High duty is generally considered as greater than 2,500 life time cycles. High duty cylinders (also known as industrial grade) are fabricated of rugged, resilient materials.

Aluminum jacks cannot be used for high cycle applications. As a rule of thumb, pumps require 20% more oil volume than jack(s) for low-cycle applications and double the oil volume of jack(s) for high-cycle applications.

Single vs. Double acting

Single Acting - Oil is pumped one way into jack to extend/raise piston out of cylinder – Either steel spring in jack OR weight of lowering load retracts/pulls down piston and pushes oil back into pump. Jacks are ideal for lifting, holding, pushing & pulling.

Double Acting - Oil is pumped two ways: (1) into jack to extend/raise piston out of cylinder and (2) out of jack to retract/push down piston and return oil back into pump. Jacks are ideal for lifting and controlled descent.

 

Single vs. Double speed

Single speed: The pump operates the jack at one and the same consistent speed.

Double Speed: With the cylinder unloaded, pump delivers a high volume of oil for fast cylinder speed. Once the load is engaged, the pump automatically switches to the slower high pressure lifting stage.

SCFM

SCFM stands for Standard Cubic Feet per Minute. It denotes how much air volume (measured in cubic feet) is needed per minute from an air supply (compressor /shop air) to operate an air over hydraulic pump.

NPTF

NPTF stands for National Pipe Thread Fine. It denotes the inside diameter of a fitting or hydraulic hose. The standard sizes are 3/8 inch NPTF (also referred to as fast flow) or 1/4 inch NPTF.

Regular size vs. Low Profile

• Regular size cylinders are tall & thin.
• Low profile cylinders are short & stubby.
• Ultra-low profile jacks are also referred to as pancake jacks or flat jacks.

Hollow Jack / Center Hole Jack

In addition to general purpose lifting or horizontal pushing, the hollow cylinder is used for pulling. The jack has a center hole that runs from the top of the ram through the bottom which can be used to pull a chain or rope through the center hole to tug, pull and create tension. This is used, for example, to tighten the wire ropes on suspended bridges.

Steel vs. Aluminum

• Steel is tougher against fatigue. It is employed under the toughest working conditions.
• Aluminum is more lightweight and its non-corrosive body holds up better to weather.