Micron Technology Turbofan User Manual
Page 13
DRAFT
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4.2.7 System
Protection
Any self-contained hydraulic system MUST be protected by a relief valve from the pres-
sure side of the pump to the reservoir. This should be of the self re-setting type.
•
For parallel running this must be set to 120 bar (1800 PSI) minimum.
•
For series chains (two motors maximum) this must be set to 220 bar (3300 PSI) mini-
mum.
It is especially important to check that all other components and hoses are suitably speci-
fied for safe working at these higher pressures.
4.2.8 Pressure Surge Prevention
When stopping the sprayheads, it is important that neither the pressure nor return lines
are suddenly closed. The inertia of the atomisers can continue to drive the motors as
pumps and produce a high back-pressure in the system. The simplest method of stopping
the sprayheads is to by-pass all oil from the pump to the reservoir, leaving the ends of the
chains of sprayheads open. If this is not practical, a non-return valve may be fitted to al-
low oil to re-circulate as the motors decelerate. This option is shown in Figs 6 and 7.
4.2.9 Speed
Regulation
The speed of all sprayheads may be regulated by means of either a pressure compensated
flow control valve or a by-pass valve between the pressure line from the pump and the
reservoir. Possible options are shown in Figs 6 and 7. The valve must be of an adequate
size to handle 70% of the maximum pump output without excessive back-pressure or
overheating.
4.2.10 Hydraulic Oil
Only specially formulated hydraulic oils should be used with Turbofan Sprayheads. En-
gine lubricating oils must never be used. Shell Tellus 32 or equivalent hydraulic oil is
recommended for most conditions but Shell Tellus 37 or equivalent should be used in
tropical climates.
4.2.11 Oil Reservoir
The oil reservoir of a self-contained system must contain sufficient hydraulic oil to pre-
vent overheating. As a rough rule, allow two litres of oil for every one litre per minute
displacement of the pump. Under tropical conditions it may be necessary to increase this
by 50%.
The return line to the reservoir must be taken to a point below the oil level to prevent
foaming. The inlet and outlet lines to the reservoir must be as far apart as possible and
not directly in line with each other. A baffle should be placed between the inlet and out-
let sides of the reservoir. The reservoir should have an air space above the oil of at least
30% of the total oil volume, or 15 cm (6 inches), whichever is greater.
4.2.12 Cooling
Overheating of the system should not be a problem if the provisions of 4.2.11 above are
followed. However, if additional cooling is required, it may be necessary to return oil to
the reservoir via a heat exchanger. Ensure that this does not cause a significant back-
pressure. The use of metal (as opposed to flexible) hydraulic lines wherever possible in
the system will also help to cool the oil.