Dixon Bayco 2180 Инструкции по обслуживанию и эксплуатации - Страница 6
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Air Relief Valve – Theory of Operation
All Dixon Bayco air relief valves are spring-loaded system-pressure
actuated devices consisting of a valve disc held in a closed position
against a valve seat by means of spring pressure. The pressure in
the system to be protected always acts on the valve disc and would
tend to open the valve, however the spring load is set so as to ensure
that the pressure in the system, at normal operating pressures, is
insufficient to open the valve. However, when the system pressure
builds to a level when the pressure load on the valve disc is equal to
the load exerted by the spring, the valve will begin to open. If the
pressure in the system were to be held at this level, the load acting to
open the valve and the spring load acting to keep the valve closed
would remain in equilibrium and the valve would be neither open nor
closed. In such circumstances the valve will tend to flutter on the
valve seat and may release a small amount of air but will not be
relieving significant pressure from the system. This point is known as
the warning pressure or cracking pressure.
If the pressure in the system continues to rise, the load acting on the
face of the valve, and tending to open the valve will also continue to
rise and will begin to exceed the load exerted by the spring, which
tends to keep the valve closed. When the opening load, due to
system pressure, exceeds the closing load, due to spring force, the
valve will open, and, as long as the system pressure remains
sufficient, will stay open. This point is known as the opening pressure
or set pressure (also referred to as rated or popping pressure). The
difference between the crack pressure and opening pressure varies
between valves and is also related to the system flow rate. However
the two should not be confused, as there is a significant difference in
pressure between the two points.
If the system pressure continues to rise, the valve will continue to
open and will relieve more and more air until the valve is fully open.
At this point the valve will be relieving close to its maximum airflow
rate, further increase in system pressure will show only relatively
minor increases in flow rate. If the system pressure decreases the
relieving airflow rate will reduce and the valve will start to close but
will not fully reseat until some pressure below the opening pressure,
this pressure is known as the reseating pressure and the difference
between the two pressures is known as "blowdown".
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2180 AIR RELIEF VALVE RK