U-V-W-X-Y-Z

بدضعیفمتوسطخوبعالی (بدون رتبه)
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U

Upper Explosive Limit (UEL):
Also called the Upper Flammable Limit. Flammable vapour or gas will only burn within a limited concentration range in air. If the mixture is too rich to burn, it is above the Upper Explosive Limit. Also see Lower Explosive Limit (LEL).

Upper Flammable Limit. See above)

V

Vacuum (vacuum pump):
Absolute vacuum is a theoretical void in which no particles exist. However, even outer space contains pressure, 10**(-19) torr. A vacuum pump is a machine which sucks in air from a closed or restricted space. The harder it works, the closer it gets to absolute vacuum. The air delivered from a vacuum pump is called ‘aspired air’.

Velocity Head:
This is best explained by analogy, imagine a fireman’s hose. The pumps are delivering water through the hose at 100 psig, however you can easily cup your hands around the water jet. Stand in front of the jet and you end up on your back. The pressure from the hose is almost entirely velocity pressure which is the same as velocity head.

Vienna Convention for the Protection of the Ozone Layer:
Set up in 1981 by the UN Governing Council, its task was to secure a general treaty to tackle ozone depletion. This proved difficult and The Vienna Convention & etc was finally signed by only 20 nations in 1985. The convention provided the way forward for future protocols, including the very important Montreal Protocol.

Volume Delivered:
This if often confused by the layman with pressure. Just because a compressor can deliver 100 psig, it doesn’t mean that it is big enough to supply the quantity of air required for a process. A bicycle pump may be able to deliver 100 psig but it can’t support the air requirements of a factory, even though the factory only needs 100 psig to operate. Volume delivered is measured in CFM or units similar.

Volumetric Efficiency:
This is the ratio between the actual volume delivered and the swept volume.

W

Water Resources Act – 1991:
This Act of Parliament defines what you can do and what you can’t do with condensate from an air compressor. The old days of simply pouring it down a drain, or even pouring on to the ground have long gone. To do so may cost you a £20,000 fine in a Magistrates Court, or even three months in jail. The act has introduced a new buzz phrase called ‘Condensate Management’.

Work in Compressed Air Regulations 1996:
This piece of legislation provides the H & S framework to manage the risks associated with personnel working inside a compressed air environment. For example, hyperbaric tunnelling systems and the like.

Written Scheme of Examination (WSE):
This is a formal procedure required under the Safety of Pressure Systems Regulations for ensuring that the entire pressurised system is safe. The procedure allows for the documentation, testing and recording of items contained within a system. The WSE must be signed off by a Competent Person.

Z

Zone:
Hazardous area classifications. For gases, we have three hazardous zones, for dusts we have two hazardous zones. For gases we have…

* Zone 2 is the lowest with an explosive mixture unlikely to occur during normal operation.
* Zone 1 is an area where an explosive mixture is likely to occur during normal production.
* Zone 0 is an area where an explosive mixture is continually (or may be continually) present.

For dust we have…

* Zone Z. An area in which combustible material is or may be present as a cloud during normal operations, is sufficient quantity to produce an explosive concentration with air.
* Zone Y. An area not classified as zone Z, in which accumulated layers of combustible material may be present under abnormal conditions, giving rise to an ignitable mixture with air.

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