37
LUNGHEZZA
VIRTUALE TRA
T
T
A
in m / VIRTUAL
LENGHT DEAL
T WITH IN METRES
LONGUER VIRTUELLE en m / VIRTUELLE LÄNGE in m / LONGITUD VIRTUAL en m.
PORTATA / FLOW / DEBIT / DURCHSATZ / CAUDAL m
3
/h
BT 1387
GAS FEED SYSTEM AT AVERAGE PRESSURE (a few bars)
(see BT 8058 - BT 8530/1 - BT 8531/1)
When high delivery is required, the Gas Distributing Company requests the installation of a unit comprising a pressure
reducer and a meter, and then connects it to the gas pipe network at average pressure (a few bars).
This unit can be supplied by the Gas Distributing Company or by the user, but should be according to the Gas
Company’s precise instructions.
The unit’s pressure reducer should be large enough to supply the maximum gas delivery required by the burner at the
rate of pressure normally estimated for it.
From experience, we would recommend utilising a large-scale reducer in order to attenuate the notable increase in
pressure which occurs when the burner comes to a standstill, with a high delivery.
(Regulations require that the gas valves close in less than one second).
As an indication, we would advise using a reducer capable of producing a delivery (m
3
/h) about double that of the
maximum amount estimated for the burner.
If several burners are to be used, each one should have its own pressure reducer; this will enable the gas feed pressure
to the burner to be maintained at a constant level even if only one burner is operating at the time.
Consequently, it is possible to accurately regulate the delivery and therefore the combustion, and thus improve yield.
The dimension of the gas pipeline should be in function with the quantity of gas it has to deliver. We advise maintaining
the load loss at a low level (not more than 10 % of the gas pressure value at the burner); it should be kept in mind that
the load loss is added to the pressure existing when the burner stops and therefore a subsequent start up will occur at
a pressure that rises in accordance with an increase in the pipe’s load loss.
Should the gas pressure reach unacceptable values when the burner stops (rapid closure of the gas valves), it is
necessary to install between the reducer and the first valve of the burner an automatic overflow valve and relative
conveying pipe, of suitable section, in the open air. The end of the conveying pipe in the open air should terminate in a
suitable place, be protected from rain and have a flame trap.
The overflow valve should be regulated in such a way as to completely unload excessive pressure.
See diagram n° BT 8058 for gas pipeline dimensions.
Near to the burner should also be fitted a cut-off ball cock, a gas filter, an anti-vibration joint and a flanged fitting (see BT
8530/1 and BT 8531/1 ).
