Goetze 455 Manual Del Usuario página 11

5
Operation / maintenance
The working pressure of the installation should be at least 10% below the closing
pressure of the safety valve. This means that the safety valve can close correctly
again after blow off. In case of minor leaks caused by impurities between the
sealing surfaces, the valve can be cleaned by lifting it up to blow off. If the leak
cannot be eliminated, the sealing surface is likely to be damaged, and this can be
repaired only in our factory or by experienced specialists. Lifting is performed by
activating the lifting lever on the valve top (fig. a). For delivery purposes the lifting
lever is blocked by means of a strap which has to be removed for actuating the
lifting device.
Safety valves without bellows ( Fig. b)
For safety valves without bellows, the maximum allowable back pressure on
the valve outlet side is 10% of the set pressure. If a continuous superimposed
back pressure exists, this has to be considered when setting the safety valve on
the manufacturer's test stand and must be notified in the order. If a higher back
pressure (including superimposed back pressure in combination with built-up back
pressure), exists, this is to be considered in the design and the manufacturer is to
be consulted.
Safety valves with metal bellows (Fig. c)
Under superimposed back pressure, the bellows have a compensating effect on the
set pressure of the safety valve. In order not to adversely affect the safe function,
the maximum allowable superimposed back pressure on the valve outlet side must
not exceed 30% of the set pressure. If a higher back pressure (including superimpo-
sed back pressure in combination with built-up back pressure), exists, this is to be
considered in the design and the manufacturer is to be consulted.
Lifting device for maintenance
In the case of safety valves with a lifting device it is recommended, and in certain
plant-specific cases even stipulated that the valves from time to time must be made
to blow-off by lifting the seal off the seat, in order to assure the correct functioning
of the safety valve. They can be opened at an operating pressure of ≥85 % of the
response pressure at the latest. The lifting device is not to be operated when in a
pressure-free state.
Safety valves represent the last point of protection for the silo or installation. They
should be capable of preventing unauthorized excess pressure when all other
upstream regulation, control and monitoring devices fail. They should be capable
of preventing unauthorized excess pressure when all other upstream regulation,
control and monitoring devices fail. The maintenance intervals for these fittings are
to be specified by the operator according to the conditions of use.
Assembly and maintenance instructions - 455, 355, 255 www.goetze-armaturen.de