Measuring vacuum - Your guide to vacuum measurement and lifting systems

Absolute vacuum and absolute pressure
In an absolute vacuum, there is no gas or other matter that can create pressure. This means that the pressure is exactly zero. Absolute pressure starts at absolute vacuum (or zero) and goes up. Absolute pressure is the sum of the measured pressure and the atmospheric pressure. Lifts All uses a simplified version to define vacuum or negative pressure as a percentage where 0% is 1 Atm or 1 bar of pressure. 40% ≈ -0.4 bar, while 60% ≈ -0.6 bar.

Atmosphere (Atm)
Atmosphere (atm) is a unit of pressure used in hydraulics and other applications. 101.325 kPa (101 325 Pa) corresponds to the normal atmospheric pressure at sea level.

Bar
Bar is a pressure unit used in meteorology, high pressure hydraulics and in diving. Lifts All's lifting tools are usually powered by 6-7 bar compressed air. 1 bar ≈ 1 Atm. 1 bar = 760 mmHg.

Mercury (mmHg)
Vacuum is often measured in millimeters (mmHg) or inches of mercury on the air pressure scale.

Pascal (Pa)
Pascal is a unit of pressure formerly known as millibar.

PSI
PSI (Pound Force per Square Inch) is a unit of pressure used primarily in the United States. 1 bar = 14 psi.

SI unit
The SI units are a standard for units of measure used in the measurement of quantities. SI units are part of the International System of Units.

Micro
Is an SI prefix.

Torr
Dry, mmHg or millimetre mercury is a unit of pressure. There is a small but insignificant difference between torr and mmHg. The pressure unit is most often used to measure vacuum or in healthcare to indicate blood pressure.

Overpressure
Pumping air into an object adds more air molecules than there are in the air outside the object. The pump compresses the air so that it is forced into the object, creating an overpressure.

Bal-Trol is the pneumatic cylinder that powers almost all Lifts All lifting tools. Bal-Trol consists of an aluminum cylinder with an encapsulated single-acting piston to which a cable is anchored. Air is connected to one end of the Bal-Trol while the other end is pressurized. When air is applied, the piston is moved back and forth, causing the lifting tool to move upwards when air is admitted and downwards when air is released. The lifting force is directly proportional to the medium pressure, which means that, for example, a ten percent increase in pressure gives a ten percent increase in lifting force. Bal-Trol's normal pressure is 6 bar +20 percent.

Bal-Trol's piston balances on a kind of air cushion, which means that there is a certain amount of wiggle room for the lifting tool to be manually adjusted in height. This is useful, for example, when an object needs to fit in very precisely. This is a big difference compared to a classic electric hoist where the lift is static.

The Bal-Trol is equipped with a check valve called an anti-jump. The non-return valve is adjusted by a spring that controls the preload. When a lifting tool loses its load, the flow of air to the Bal-Trol's piston becomes too great and the tool moves upwards. The check valve then closes, which means that the spring is unable to resist. This builds up pressure that brakes the tool.

The load monitor is a valve that senses the pressure in the cylinder, a pressure that is set to be slightly higher than what the gripper generates in the Bal-Trol. When you lift the load with the gripper, the pressure increases, which the load monitor senses and reacts by disconnecting the air release button. This means that it becomes impossible to release the load once it is in the air. When the load is set down on a surface, the pressure drops and it becomes possible to release the load.

The load monitor controls the Bal-Trol lifting safety system. On mechanical grippers there is a sensor that detects whether the load is secure. On a vacuum gripper there is a vacuum sensor that detects that the tool has reached a certain vacuum level when the cups are attached. Then the load can be lifted. But if the operator tries to lift without a green light and the guard reacts, the air to the PSH control is cut off and the up button can no longer be used, only lowering is possible.

When designing a vacuum system (a lifting tool), it is important to adapt the tool to the object being lifted. Lifts All’s lifters or gripper using either a mechanical grip vacuum cups, or a combination of both. In this text, we focus on lifting using vacuum.

Vacuum means that the pressure is lower than atmospheric pressure. To create a pressure lower than atmospheric pressure, air mass must be removed with a vacuum pump. The air evacuated per unit time is called vacuum flow and is a measure of how fast the pump can evacuate the air. To determine the vacuum level, the negative pressure in the vacuum cup or base is measured.

The vacuum pump creates a vacuum flow in the suction cups by evacuating the air inside them, while the atmospheric pressure from outside pushes the cup downwards, causing it to be sucked in. When the suction cups are attached to a porous material, it is impossible to evacuate all the air, as the porous material is constantly leaking in new air. Therefore, it is necessary to compensate the leakage by creating a higher vacuum flow with a vacuum pump dimensioned for this.
For airtight objects, the capacity of the vacuum pump depends on how fast the system can evacuate air to a specific vacuum level. To create an efficient lift, the choice of articulated jib cranes needs to be carefully considered: type, size and number, as well as which ejector should be used. The surface area covered by the vacuum cup is more important than the height of the cup.