Some of them are technically required, while others help to improve our website for you.

The compressed air is supplied through connection (A) to ejectors.

After passing through the nozzle, the accelerated air slows down once again and a vacuum is created.

The volumes of the individual nozzles add up to form a total suction rate.

This function interrupts vacuum generation as soon as a safe vacuum value has been reached.

Vacuum generation is switched back on only once the value falls below the preset minimum vacuum value.

Compact ejectors with an air-saving regulation use far less compressed air than a conventional vacuum ejector.

In fact, it is actually lowered by increasing the motive fluid pressure.

They are especially effective in the chemical industry where an on-site supply of the high-pressure motive gas is available.

Very often, the motive fluid is steam and the device is called a steam jet ejector.

Basic ejector components are the steam chest, nozzle, suction, throat, diffuser and they discharge (Fig.

In the compressors recycle waste steam and low-pressure water vapor discharge, reducing energy consumption by 30 or more.

They are applied in processes such as crystallization, deaeration, drying, cooling, high vacuum distillation and deodorization.

Single-nozzle units are also available with an automatic spindle for special applications.

The single-nozzle, fixed orifice is the simplest type of ejector.

They usually save as much as 10 to 20 in motive steam, compared with single-nozzle units designed for the same conditions.

In this case, the spindle is essentially changing the dimensions of the ejectors internalities is, creating a new single-point design.

For this reason, the spindle-operated ejector provides high off-design efficiency, which is very handy if operating conditions must vary.

Sometimes precondensers, booster condensers and aftercondensers are also used.

The size and type of condenser selected is a function of air-vapor ratios, cooling water temperatures available, steam and water costs, and contaminants in the suction vapor.

However, users should be aware that the barometric condenser is a direct-contact design.

The cooling water is mixed directly with the vapor to be condensed.

If there are any environmental considerations concerning the process fluid, it should not be mixed with cooling water.

No contamination can occur; thus, the condenser water is cooled and reused.

On the other hand, the shell-and-tube design may require more maintenance due to the possibility of scale or solids buildup on the condenser tubes.

This results in a decrease in pressure and an increase in velocity.

The motive fluid, which is now at high velocity, entrains the suction fluid and combines with it.

Potential energy is converted to kinetic energy; thus, velocity increases and pressure decreases.

The mixture reaches its maximum velocity and lowest pressure at the Venturi throat (Fig.

The fluid then is charges at an intermediate pressure, which is higher than the inlet suction fluid pressure, but much lower than the inlet motive fluid pressure.

That is, its optimum efficiency exists at a single set of conditions.

The specifications for which it is designed represent the maximum capacity built into the unit.

Critical flow means the fluid velocity in the diffuser throat is sonic.

Ejector Vacuum System Design