Part-20 Washwater Systems

20 WASHWATER SYSTEMS ............................................................................. 2
20.1 GENERAL ...................................................................................................... 2
20.1.1 Scope 2
20.1.2 References 2
20.1.3 Submittals 2
20.2 PRODUCTS ................................................................................................... 2
20.2.1 General 2
20.2.2 Washwater Booster Set 2
20.3 TESTING ....................................................................................................... 3
20.4 INSTALLATION AND COMMISSIONING ...................................................... 3

20 WASHWATER SYSTEMS
20.1 GENERAL

20.1.1 Scope
1 This part specifies the requirement for the design, manufacture, testing and commissioning of washwater systems.

2 Related Sections and Parts are as follows:

Section 1 General
Section 8 Drainage Works
Section 10 Instrumentation, Control and Automation
Section 13 Building Electrical Works
Section 21 Electrical Works
20.1.2 References
1 The following standards or revised/updated versions are referred to in this part:

BS 970 (ISO 683) ....... Wrought steels for mechanical and allied engineering purposes
BS 1123 ..................... Safety valves, gauges and fusible plugs for compressed air or inert gas installation
BS 5169 ..................... Specification for fusion welded steel air receivers
PD 5500 .................... Specification for unfired fusion welded pressure vessels

ISO 10474 .................. Steel & Steel Products Inspection Documents

List of ‘Approved Suppliers’ prepared by the Public Works Authority
20.1.3 Submittals
1 In addition to the requirements of Part 1 of this Section, the Contractor shall reconfirm the information provided in the Technical Submission Schedules submitted with his Tender.

20.2 PRODUCTS

20.2.1 General
1 The wash water system shall be capable of delivering a supply of final effluent wash water to the plant at the rate recommended by the manufacturers of the proprietary equipment plus a minimum of 6 l/s at 4 bar(g) with any two hydrants open and all process water requirements being meet simultaneously.

2 The design shall ensure that the hydrant pressure does not exceed 5 bar. Pressure reducing valves may be utilised for this purpose.

20.2.2 Washwater Booster Set
1 The wash water system shall comprise a minimum of one duty pump and a standby pump, pressure vessel with adjustable differential pressure switches, interconnecting pipework and valves, and a terminal panel. The motor starters and controls shall be part of a FBA. The pumps shall be provided with a duplex-strainer in the suction piping to prevent any debris from entering the system.

2 The pressure vessel shall be adequately sized to keep the maximum number of pump starts under the worst conditions to 15 per hour. The pressure vessel shall incorporate a butyl-rubber diaphragm to contain the water and shall be charged with nitrogen or another approved inert gas.

3 The vessel shall be of welded construction and in accordance with the relevant British Standards or ASME VII Div 1, and shall be complete with all necessary fixtures and fittings and shall include the following:-

(a) Inspection manhole single or double bridged, according to size, which shall seat on pressure.

(b) Flanged inlet and outlet connections.

(d) Safety valve, to relieve excess air pressure in tank to atmosphere.

(e) 50mm drain connection with valve.

4 The vessel shall be high quality epoxy coated inside and out after all manufacture has been completed, and shall be suitable for the maximum working pressure required by the process.

5 The upper dome of the vessel shall be fitted with a suitable spring loaded pressure relief valve, which shall be arranged to commence to open at 110% of the maximum system working pressure, and be fully open at 120% of this pressure.

6 The pressure vessel, which shall be of vertical or horizontal construction, shall be mounted on a minimum of four mounting feet, to raise the vessel off the base plate a distance of not less than 300mm.

7 The vessel shall be fitted with a 150mm diameter pressure gauge, connected such that it reads the air pressure in the vessel and thereby indicating the pressure in the system.

8 There shall be provided for the vessel a manually operated air release valve, to enable the system to be depressurised to atmosphere before the system is drained and to enable the vessel to be recharged.

9 Pressure switches shall be robustly constructed and suitable for the arduous duties involved, and shall be fully adjustable over their working range, together with adjustable differentials.

20.3 TESTING

1 1 Testing of the vessel to the recommended Code of Practice shall be carried out at the manufacturers works, and a test certificate shall be issued. The working and test pressures shall be stamped onto the outside of the vessel such that they are clearly visible.

20.4 INSTALLATION AND COMMISSIONING

1 Installation and commissioning shall be in accordance with Part 1 of this Section 9.

END OF PART