Micron Technology Turbofan DRAFT 4.2.7System Protection, Pressure Surge Prevention, Hydraulic Oil

DRAFT

4.2.7System 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.

4.2.9Speed 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.

4.2.11Oil 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.

4.2.12Cooling

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.

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