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Hoval STU Wood Pellet Boiler
Maintenance - Inspection & Servicing
Pick-Up Auger (Bunker Worm)
Covering/Changing Pick-Up Slots - Where fitted
The pick-up auger and tube also incorporates the flange type mounting for the worm drive motor and integral shear cover. The tube is
bracketed in the bunker and sleeved into a swing tube. This allows the tube to be turned, enabling the pick up slot to be closed off and
the tube to be run empty - or an alternate pick-up slot selected.
To do this, release the retaining clip and turn the tube using the turning bar provided. There are 2 grease nipples fitted to the pick-up
tube and bearing (see drawing). One is fitted on the side of the Swing Tube; this should be greased periodically to aid turning the pick-
up tube. The other can be found on the pick-up bearing housing next to the Shear Pin Assembly; this should be greased on a regular
basis in order to prevent dust passing through the bearing into the boilerhouse (Grease Gun supplied). To spread the grease evenly
throughout the bearing, pump grease in while the motor is running.
Delivery and Pick-Up Augers (worms)
Both worms are fitted with shear pin couplings, this connects the worm to the drive motor via a Brass Shear Pin. In the event of a jam,
the brass pin will break and allow the motor to carry on turning undamaged.
To repair a broken shear pin drive the motor so that the shear pin slot is at the top, using the shear pin bar provided, align the slot on
the worm section, remove broken pin and fit replacement. If there is a jam or pin failure on the Pick-Up Auger always check the Delivery
Auger and the condition of the shear pin in the Delivery Auger - it may well have broken first and caused the Pick-Up pin to shear.
N.B. If you are unable to turn the worm section or the replaced pin breaks straight away,
contact Hoval Service
.
Forced Draught (FD) Fan
This fan is floor mounted next to the stoker and supplies combustion air to the stoker. There are two dampers on the air inlet, one has a
modulating motor fitted to it and the other has a manual adjustment on it. There are set at the same time as commissioning and should
only be adjusted by a suitably qualified engineer.
Induced Draught (ID) Fan
This fan is fitted at the rear of the boiler between the smoke box and the chimney. There is also a fully modulating motorised damper fit-
ted in the duct work between the boiler and the ID fan. The motorised damper is controlled by a preset pressure switch keeping a nega-
tive pressure over the fire. The drive from the motor to the fan is via 2x fan belts, these require checking during servicing and changing
if necessary.
In addition to the shear pin protection all drive motors are
protected via thermal overload relays in the control panel; this
gives the added protection in the event of a gradual worm jam. If a
motor has tripped its thermal overload a warning light will be
illuminated on the front of the panel.
