Guide: Glossary, Units, and Scales for Vacuum

Absolute Vacuum and Vacuum Pressure

An absolute vacuum is space void of air. It has no gas or other matter to create pressure: absolute vacuum is when pressure is zero. Absolute pressure begins at zero (absolute vacuum) and increases. Absolute pressure is the sum of the measured pressure and atmospheric pressure.
Lifts All defines vacuum or negative pressure as a percentage where 0% is 1 Atm or 1 bar. For example, 40% is approximately -0.4 bar, while 60% is about -0.6 bar.

Atmosphere (Atm)

An atmosphere (Atm) is a pressure unit commonly used in areas such as hydraulics. One Atm unit is equivalent to the average air pressure at sea level at a temperature of 15 degrees Celsius (59 degrees Fahrenheit). One atmosphere is 101,325 kPa (101,325 Pa). Standard atmospheric pressure serves as a reference point for various pressure measurements, including Torr and mmHg, and is crucial for understanding different levels of pressure and vacuum states.

Bar

Bar is a unit of pressure used in meteorology, high-pressure hydraulics, and diving. Lifts All’s lifting tools typically operate at 6-7 bar of compressed air. 1 bar ≈ 1 Atm, and 1 bar = 760 mmHg.

Gauge Pressure

By pumping air into an object, you add more air molecules than in the surrounding air. The pump compresses the air into the object, creating gauge pressure, which is measured relative to ambient atmospheric pressure. Understanding vacuum levels in different units such as Torr, mbar, and Pascal is crucial for technicians monitoring vacuum systems, as inconsistent pressure measurements can significantly affect system performance and user perceptions.

Micro

Micro is an SI prefix for units.

Millimeters of Mercury (mmHg) and Inches of Mercury

Vacuum pressure is often measured in millimeters of mercury (mmHg) or inches of mercury on the pressure scale. Vacuum pressure measured in mmHg is used in various applications, including scientific research, industrial processes, and medical devices, to ensure precise control and standardization.

Pascal (Pa)

Pascal is a unit of pressure previously called the millibar.

PSI (Pounds per Square Inch)

PSI is a unit of pressure primarily used in the United States. 1 bar = 14 psi.

SI Units

SI units are standardized measurement units used internationally to quantify values.

Torr

Torr, mmHg, or millimeters of mercury is a pressure unit. Although there is a slight difference between Torr and mmHg, it is negligible. This unit is often used for measuring vacuum or for blood pressure in healthcare.

Pneumatic Lifting System – Lifting with Compressed Air and Vacuum Systems

Bal-Trol

‘Bal-Trol’ is the pneumatic cylinder that powers nearly all of Lifts All’s lifting tools. It consists of an aluminum cylinder with an encapsulated single-acting piston anchored to a cable. Compressed air is applied to one end of the Bal-Trol, while the other end remains at atmospheric pressure. When air is supplied, the piston moves back and forth, raising the lifting tool as air is introduced and lowering it as air is released. The lifting force is directly proportional to the air pressure, for example, a 10% increase in pressure yields a 10% increase in lifting power. The standard operating pressure for Bal-Trol is 6 bar, with a tolerance of +20%.

The Bal-Trol piston rests against a cushion of air in the cylinder. This air cushion allows certain flexibility for manual adjustments to the height of the lifting tool, which is practical for precise positioning and unlike traditional electric hoists that are static.

Anti-Jump

The Bal-Trol features a check valve, or anti-jump mechanism, controlled by a spring that adjusts the preload. If the load on a lifting tool is intentionally or unintentionally knocked off, excess airflow to the Bal-Trol piston will cause the tool to jump upwards. In this case, the check valve closes, the spring no longer resists the flow, and pressure builds up to stop the tool’s upward jostle.

Load Guard

The load guard is a valve that gauges the pressure in the cylinder, calibrated slightly above what the gripper exerts in the Bal-Trol. When a load is lifted, the pressure rises triggering the load guard to disconnect airflow to the ‘release’ button. This safety feature ensures that the load cannot be released while suspended in the air. When the load is placed down, the pressure drops, allowing airflow back into the ‘release button and the operator can then release the load.

Lifting Safety System

The load guard regulates the Bal-Trol’s Lifting Safety system. Mechanical grippers are equipped with a sensor to confirm that the load is secure, while vacuum grippers have a vacuum sensor to detect when the tool has reached a specific vacuum level upon attachment. Only then can the load be lifted. If the operator attempts to lift without receiving a green-light signal from the load guard, airflow to the PSH control is cut off, disabling the ‘up’ lever and allowing only downward movement.

Vacuum Gripping

When designing a vacuum-based lifting system, it’s important to adapt the tool to the object being lifted. Lifts All’s lifting tools or grippers can lift either with mechanical means, vacuum cups, or a combination of both. The following section focuses on lifting with vacuum-based grippers.

What is Vacuum and How is it Measured?

Vacuum occurs when the pressure is lower than atmospheric pressure. To achieve this, air must be removed using a vacuum pump. The evacuated air per unit of time is known as vacuum flow and is a measurement of the pump’s efficiency. To determine the vacuum level, the negative pressure is measured in the vacuum cup or vacuum application.

Porous vs. Airtight Loads

The vacuum pump creates a vacuum flow in the suction cups by expelling the air inside, while atmospheric pressure pushes the cup downward, securing it to the object. When suction cups are placed on to a load made of porous material, some air will always seep through, preventing complete expulsion of air. In these cases, a vacuum pump with higher capacity is required to offset the continuous air leakage.
For airtight objects, the pump’s capacity is dependent on how quickly it can expel air to achieve a specific vacuum level. Effective lifting depends on choosing the right suction cups – type, size, and number – and choosing an appropriate ejector. The surface area covered by the vacuum cups is crucial for safe gripping.