In this sample MEP specification section, Mechanical General Plant and Machines have been described in detail under construction contract work.
1. Circulating Pumps
1.1 General Requirements for Circulating Pumps
Estimated pump duties are given in the Particular Specification, but it is the Contractor’s responsibility to re-calculate duties based on his installation drawings and selected pipeline equipment, and to provide pumps capable of delivering the required water quantity and pressure, and operating satisfactorily under the conditions involved.
Circulating pumps generally shall be of the single stage end suction vertical split casing type direct driven through a flexible coupling by a totally enclosed fan cooled British Standard metric electric motor running at 1450 rpm, the whole mounted on a cast iron or fabricated mild steel base. The motor shall be sized to avoid overload at any operating point on the pump curve.
Closed-coupled or belt-driven pumps will not be permitted unless specified elsewhere.
Anti-vibration protection and flexible connections shall be provided using methods detailed in relevant clause.
All pumps shall be fully tested at works, with performance characteristics guaranteed in accordance with BS 5316 Part 1.
1.2 General Construction for Circulating Pumps
Pumps shall normally be constructed with cast iron casing, bronze impeller and stainless steel shaft running in a pair of pedestal mounted heavy duty sealed for-life ball bearings.
All pumps shall be fitted with mechanical seals of the self-adjusting type, suitable for the particular operating temperature and pressure.
The exposed motor and pump shafts and the flexible coupling shall be protected by a galvanised wire mesh guard.
2. Water Storage Tank
Water tanks of 1000 litres capacity and above shall be constructed from hot pressed and cured GRP panels 1000mm x 1000mm or 1000mm x 500mm, with external base flanges, external side flanges and internal roof flanges.
The panel materials shall be UV stabilised, and light-proof and shall have a minimum glass content of 30%. The coefficient of water absorption shall be less than 0.2%.
The tank shall be supplied with all necessary internal stays and bracing, all such material being of stainless steel where in contact with the water.
The panels shall be assembled by means of galvanised steel nuts, bolts and washers, and foamed PVC gaskets.
The tank shall be provided with a sealed roof capable of withstanding the load imposed by a man walking on top of the tank, and complete with 600mm dia. hinged and bolted sealed manhole and 100mm dia., screened air vent.
Gunmetal screwed or PVC flanged pipe connections shall be provided as required.
Tanks exceeding 1000mm in depth shall be provided with a PVC internal ladder and galvanised steel external ladder. The tank shall be erected on a steel skid base, which shall be supplied by the tank manufacturer.
Water tanks of less than 1000 litres capacity shall be of one-piece moulded GRP construction with loose cover. The material used shall be UV stabilised, of ample thickness for the water pressure involved, and shall incorporate a central black light-proof layer. The inside surface of the tank shall be finished smooth.
3. Water Level Indication
Remote reading hydrostatic contents gauges calibrated in litres shall be fitted to all water storage tanks of 1000 litres capacity or above. The gauges shall comprise transmitter, capillary tubing and 150mm dia dial indicator mounted in a position to be agreed with the Engineer.
4. Immersion Heaters for Hot Water Services
The immersion heaters for hot water cylinders shall be of the electrical loadings indicated. The heating elements shall be heavy duty with corrosion resistant sheath, and shall be removable without draining the cylinder.
The heaters shall be suitable for horizontal or vertical mounting with a flanged connection for bolting to the cylinder mating flange, and the immersed length shall be compatible with the cylinder to which it is fitted.
Wiring from the elements shall be brought to a dust-tight terminal box with removable cover, which shall be an integral part of the heater.
A thermostat shall be provided with each heater and this shall be pre-set to control the temperature of the water in the cylinder to that indicated in the Schedules. There shall be provision for replacement of the thermostat without draining the cylinder to which it is fitted. All immersion heaters of 9 kW rating and above shall be complete with suitably rated triple pole air break contactor with neutral link and 220 V.a.c. operating coil which shall be controlled by the heater thermostat.
5. Direct Electric Water Heaters
5.1 Pressure Type for Vented Systems
Horizontal or vertical cylindrical type, with water container constructed from copper or alternatively steel with an accepted corrosion resistant inner lining.
An outer casing of enamelled steel shall be provided with the space between the water container and outer casing filled with a minimum of 25mm of polyurethane foam insulation.
Each unit shall be tested at Works to 1½ times the working pressure, and a test certificate issued.
Immersion heaters and thermostats shall be provided as Clause 803.4, and the capacities and duties shall be as indicated in the Particular Specification.
Tappings shall be provided of the same size as the connecting pipework.
5.2 High Pressure Type for Unvented Systems
As for vented systems, but the water container must be of lined steel, and the test pressure must be a minimum of 10.5 bar. In addition an accepted pressure safety device must be fitted, with the discharge piped direct into the drainage system, and an anti-vacuum valve.
6. Expansion Vessels
Expansion vessels shall be of the membrane type, comprising a welded mild steel cylindrical pressure vessel with internal rubber diaphragm to separate the water from the pressurising gas. The pressure vessel shall be manufactured in accordance with BS4814, suitable for a maximum working pressure of 16 bar. The diaphragm shall be of the removable rubber bag type, and the internal surface of the vessel where in contact with the diaphragm shall be treated with an epoxy/polyester coating. The pressurising gas shall be Nitrogen.
The vessel shall be provided with the following fittings:-
- Pressure gauge.
- Pressure relief valve.
- Support legs or cradle.
- 150mm dia. bolted inspection cover.
- Flanged or screwed inlet connection.
- Nitrogen fill valve.
- Inspection window (sizes 500 litre and above)
- Lifting eye (sizes 500 litre and above)
Expansion vessels shall be selected by the Contractor according to the actual calculated system volume, temperature variations and specified working pressures.
