VACUVENT VA Series, Руководство пользователя

Страница: 14 / 18

Independent Valve Marketing (Pty) Ltd
Engineering Page 14 of 18
VSS0203WD00
STORAGE
All Vacuvent air valves should be stored in a moderately cool area free from debris. If debris cannot
be avoided, simply wrapping the air valve in plastic should be sufficient to prevent debris from
entering the internal mechanisms of the air valve.
OPERATION AND SIZING
GENERAL SIZING
BASIC OPERATION
Vacuvent have full valve size intakes (large orifices) but control the exhaust exclusively via the Anti-
Shock orifices.
No exhaust is vented via the large orifice and this function is specifically designed for (for further
reading, see technical information). This valve range covers most applications as standard but still
allows the designer some scope to specify more accurately.
BASIC PRINCIPLES
When a section drains down, the air valve at the apex must be sized to protect the pipe and seals
until the next valve lower down opens. So intake cannot be calculated by adding all the valves on
that section. Exhaust however is another matter and it’s feasible in some instances to add all the
anti-shock capabilities for one section. It’s also important to ensure that enough head (including
dynamic) is available to seal the valve off otherwise a syphon valve may be required. This is a
consideration on pumping systems where the final section after the apex has the possibility of
draining down faster than the pumping rate. Another factor is the differentiation between designed
flow rates and possible drainage rates. Drainage rates are generally estimated 2 times the designed
flow rates i.e. 1-2 m/sec flow rate and say 2-4 m/sec drainage. If the pipe is to be protected from
vacuum, generally the exhaust capability is more than adequate
PLACEMENT
The graphic shows most of the common places where air release valves are fitted. High points are a
natural start, also where the pipeline crosses obstacles like rivers and roads. Check for syphon
application above the hydraulic grade line. To control pump start and pump trip, air release valves
should be placed before and after the check valve.