Goetze 451 P/PL Manual Del Usuario página 9

5 Operating and Maintenance
The operating pressure of the plant is to be at least 5 % lower than the closing pressure of
the safety valve. In this way, the valve can satisfactorily close again after blowing off.
In the event of minor leaks, which may be caused by contamination between the sealing
surfaces, the valve can be made to blow off through lifting, for cleaning purposes. If this
does not remove the leak, the sealing surface is probably damaged and this can only be
repaired at our factory or by authorized specialists. Depending on the version, lifting is either
carried out by means of a knurled nut above the spring bonnet (Fig. 1) which is turned coun-
terclockwise (afterwards the knurled nut has to be turned back to the stop) or by actuating
the lifting lever on the upper part of the valve (Fig. 2). 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
In addition, in the case of safety valves without bellows (Fig. 4), the entire upper part can
be unscrewed from the housing using appropriate tools and any residue removed from the
seat and the seat sealing.
Prior to removal make sure that the safety valve is not under pressure.
The response pressure of the safety valve is not altered through the reassembly of the
upper part in the housing.
Safety valves with metal bellows
In the case of safety valves with metal bellows (Fig. 3) the upper part is not to be sepa-
rated from the housing, because otherwise tightness is no longer guaranteed in the event
of backpressure occurring.
Safety valves with gas-tight cap
On safety valves with gas-tight cap, the top part may not be separated from the housing
as this compromises gas tightness. However, if the top part does have to be unscrewed for
a repair, it should be ensured that the tension on the spring is released before dismantling.
You should also check before dismantling the valve whether there is any medium in the cap
and if so, what it is. Potential risk of chemical burns or poisoning.
Lifting for maintenance purposes
It is recommended, and in the case of some regulations is actually specified, that on safety
valves with a lifting device the safety valve should be made to blow off by lifting, at inter-
vals to suit the system in question, to assure the function of the safety valve. This is why
they can be made to open at the latest as from an operating pressure of ≥ 85% of the
response pressure. The lifting device is not to be operated when in a pressure-free state.
In steam generating equipment, testing the ease of movement of safety valves must be
carried at least every 4 weeks in compliance with TRD 601. Safety valves are the ultimate
safety device for the tank or system. They must be able to prevent impermissible overpres-
sure even when all other upstream control and monitoring equipment fail. To ensure these
characteristics safety valves require maintenance, just like any other technical device. The
maintenance intervals are determined by the operator in dependence of the operating
conditions.