Ejector
The ejector is a crucial piece of equipment for proper operation of a vacuum gas feed system. The system as a whole cannot operate if the ejector does not function. This technical bulletin will provide important information on ejector selection and system design. This document will mention water operated chlorine gas ejectors for simplicity, but ejectors can be operated by air or Nitrogen and various gas and ejectors can be used to inject various gas and liquid chemicals.
Function -:
An ejector has several very important functions within the gas feed system. It needs to generate the operating vacuum, create the chlorine solution, and prevent the back flow of water into the vacuum lines. Operating Vacuum—SHITAL ENTERPRISES’ ejectors are designed to generate a vacuum of 25” mercury (Hg) or greater and generate sufficient suction to achieve the stated feed rate. Inadequate vacuum can produce unreliable gas feed. Chlorine Solution—The ejector is where the chemical is injected into the water stream. Back Flow Prevention—A check valve prevents back flow of water during shut down.
Operation A vacuum of 25” Hg or greater is generated by supply water passing through the ejectors venturi nozzle. As the supply water under high pressure is passed through a small orifice its velocity increases resulting in a drop in pressure. By creating an adequate pressure differential (ΔP) of water between the ejector inlet (supply pressure, Psupply) and the ejector outlet, this pressure drop becomes great enough to create a vacuum and draw the feed chemical through the system and into the water stream. If this pressure differential is not maintained, an insufficient vacuum will be produced or no vacuum at all.
Design SHITAL ENTERPRISES’ ejectors consist of the following common components:
- • Water inlet & solution outlet
- • One piece nozzle or nozzle/throat combination
- • Vacuum connection for gas inlet
- • Check valve
Hydraulics The combined pressure at the point of application and piping friction loss is known as the back pressure. A higher back pressure requires a higher ejector inlet pressure and more supply water to make the ejector function correctly.
Hydraulic operation curves have been developed to assist with system design. These curves specify minimum supply pressures and flow rates to be supplied to the ejector against a given back pressure.
Ejector Selection Hydro Instruments offers a wide range of ejectors to meet individual application needs. Choosing the right ejector is very important for proper and reliable operation of the gas feed system. Should the wrong ejector be chosen, problematic system operation and unwanted downtime can be the result. Ejectors for specific applications (e.g. variable orifice, anti-siphon and diaphragm-less) can enhance performance, safety and/or minimize maintenance requirements.