Spirax Sarco FT 43 Series, Installation And Maintenance Instructions Manual

Page: 13 / 28

IM-IBR17-49IN Issue 1 13
Fig. 6 Slow speed cylinder drainage with system unit
Air vent
Float
trap
Sight
glass
Condensate out
Strainer
Air bottle
Cylinder
3.6
Float traps should be fitted as close to the outlet of the plant to be drained as possible
otherwise the trap can steam lock. Steam locking occurs when the pipe between the
condensate outlet and the steam trap fills with steam and prevents condensate from
reaching the trap. This can lead to the system waterlogging which will affect plant
efficiency. It is very similar to the air locking experienced in water systems.
The most common application where steam locking is a risk is on rotating cylinders
and other applications where condensate is removed via a dip tube or siphon pipe.
Steam locking can easily be prevented by fitting the trap with a combined thermostatic
air vent and an adjustable needle valve (SLR), Figure 6 shows an FT-C trap fitted on
a slow speed cylinder.
The adjustable needle valve (SLR) is opened by turning the spindle anticlockwise. The
standard factory setting is ½ turn which equates to an approximate steam 'bypass' of
22 kg / h @ 10 bar.
Site adjustment of the adjustable needle valve can be achieved by turning anticlockwise
to increase the bypass flow, and clockwise to reduce the flow.
When draining from a high speed cylinder application, there is need for large amounts
of blow-through steam to assist the flow of condensate out of the cylinder via the
siphon tube.
In such cases the adjustable needle valve cannot handle such large amounts and an
external bypass with an adjustable needle valve is required. See Figure 7 (page 18).