Injector
From Wikipedia, the free encyclopedia
The word injector can mean:-
- A pump-like device without moving parts which charges a steam boiler or other pressure container: see below.
- Sometimes used for medical hypodermic devices: see syringe and jet injector.
- A type of oxy-gas torch.
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The injector is a pump-like device without rotating parts or a pump piston, which charges or discharges containers under pressure with suitable arrangements. It was invented by Henri Giffard in 1858. Motive force is gained at the inlet from a suitable fluid that is under pressure. By contrast, an ejector is a device that discharges fluids from containers, usually into the atmosphere. See also: eductor-jet pump.
[edit] Construction
The adjacent diagram shows the basic construction of an injector. It consists of a tapered nozzle, a throat section with surrounding box and an diffuser outlet nozzle. Air, steam or water at high pressure provides the motive force at the inlet.
[edit] How it works
The Venturi effect, a particular case of Bernoulli's principle, applies to the operation of this device. Fluid under high pressure is converted into a high velocity jet at the throat with a drop in pressure; this depends on the design of the nozzle. Fluid is sucked out of the container and the jet forces the mix through the diffuser nozzle under pressure. At the throat the inlet pressure head is converted to velocity head - the pressure energy at the inlet is converted to kinetic energy at the throat - then back to pressure energy at the outlet of the diffuser following the aforementioned principle.
In the case of the ejector, the same principle is adopted but the discharge at the diffuser nozzle is slightly more than the surrounding atmospheric pressure.
Referring now to the illustration of Giffard's injector to the right the explanation of how it works is as follows. Steam from the boiler arrives through pipe A and is controlled and regulated by a needle valve B controlled by handle C. Water arrives through the water feed pipe E. When the needle valve is opened, steam rushes through the cone D and the depression caused by the Venturi effect sucks in water from the water feed pipe E. In this cone the steam and the water mix thoroughly which results in the steam condensing and all of the kinetic energy is transferred to the water which results in a jet of water with extremely high speed rushing through F and into the receiving cone G. This creates enough pressure in the receiving pipe H to overcome the boiler pressure and lift check valve K. Once this process has been perfectly established it will be sustained and all of the water jet from F will enter G and there is no need for an overflow waste pipe. Under these circumstances F and G could be joined in a continuous tube. But there are conditions which result in an imperfect process and a part or all of the water does not have the energy to enter the boiler. This can be the result of various conditions like insufficient steam speed, imperfect steam condensation or others. Under these conditions, if the gap F-G did not exist, the pressure at that point would rise and the process could not be started again. If water is leaking at the overflow pipe during normal operation it means something is not quite right and injector operation should be checked.
[edit] Uses
This system was originally used in locomotive boilers for injecting or pumping the water to and from the boiler. For small, stationary, low pressure boilers, the injector was used to inject chemicals into the boiler drum and to suck the boiler feed pumps. In large modern boilers (measured in terms of steam production capacity) of great pressure, usage of injectors for chemical dosing is not possible due to their limited outlet pressures. However, usage in various other industries has become quite common due to their relative simplicity and adaptability due to this, for example the bulk handling of products in grains. In thermal power stations they are used for the removal for disposal of the boiler ash and the removal of fly ash from the hoppers of dust separators for the same purpose. The construction industry uses these for pumping turbid water and slurry. In everyday life, civilian fire departments use a tapered nozzle to give a high velocity water jet.
[edit] External links
[edit] See also
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