Operating instructions
31
5603 882 - 01 
Pyrotec Installation & Operating
Mechanical
Back-burn safeguard for the fuel supply system
The fire extinguishing system for the conveyor auger and 
the down pipe depends on specific requirements (location, 
size of the fuel storage site, material, pressure conditions 
and regulations), these being accessories to the scope 
of delivery ordered from Viessmann according to their 
descriptions.
Automatic triggering system for the fuel supply system 
Approved in part as a variation to the shut-off valve in 
pressure-less fuel storage units.
Slide valve
The slide valve is approved in pressure-less fuel storage 
units and is a suitable safeguard against back-burn.
The slide valve is optional and closes in case of standstill, 
danger of back-burn, or power failure with the help of a 
spring return motor.
We recommend installing a rotary valve for the PYROTEC 
Grate Firing System. In addition to being a safeguard 
against back-burn, this will also prevent any penetration 
by air leaking in via the in-feed auger.
Rotary valve
The rotary valve is optional and used if remnant wood 
is moved into fuel storage spaces with blowers, then, in 
order to reduce pressure applied, at least one rotary valve 
is necessary to reduce pressure between the fuel storage 
unit and the boiler. The rotary valve is suited to reduce 
pressure and at the same time is considered a suitable 
safeguard against back-burn.  
Max. overpressure allowed in fuel storage unit:  
+500 Pa / +2.00”wc.
Max. negative pressure allowed in fuel storage unit: 
+0 Pa / +0”wc.
 Fire Protection (continued)
IMPORTANT
IMPORTANT
IMPORTANT
Double rotary valve with pressure compensation system
If, due to special circumstances, any mechanically 
produced negative pressures or extraordinarily high 
overpressures are expected in the fuel storage unit, 
then two rotary valves must be installed in the material 
transport route according to the respective project plan 
with a pressure compensation line to the outdoors.
Max. overpressure allowed in fuel storage unit:
+3000 Pa /+12”wc.
Max. negative pressure allowed in fuel storage unit:
-3000 Pa / –12”wc.
The supplier of the silo must confirm the maximum weight 
that is to be expected on the rotary valve.
The rotary valve below the silo extraction system can 
become leaky due to wear of the sealing elements or 
through large pieces of wood that cannot be conveyed. 
This leakage can make it possible for low-temperature 
gases to flow back from the boiler into the silo.
A smoke alarm must be installed between the rotary 
valve and the silo extraction system, which, when 
triggered, will disconnect the system and create negative 
pressure in the silo.
Down pipe
A vertical drop-off section interrupts the connected line 
of burning material.
Fire protection for fuel storage space
Viessmann does not provide fire protection for the fuel 
storage space.
The local building codes and regulations must be followed 
by the heating contractor.










