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Central Heating Part 3


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Central Heating Part 1 plumbing revision to be done with exams at

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Central Heating Part 3

  2. 2. By the end of this Part you should be able to, Identify the Following components of heating systems: • Cisterns • Air separators • Circulating pumps. PRACTICE PLUMBING EXAMS © WWW.PRACTICEPLUMBINGEXAMS.COM
  3. 3. • The feed and expansion (F&E) cistern is to be used on open-vented central heating systems. • The main porous is to allow the system to be open to atmospheric pressure, allow for expansion and feed the central heating system. • The water should be set low to allow 4 % expansion + 25 mm so that the open vent is not submersed in the water. • • The cold feed from the F&E cistern to system is 15 mm minimum, and this pipe should not include any valves. • . • A servicing valve should be located on the cold water inlet pipework to the F&E cistern. PRACTICE PLUMBING EXAMS © WWW.PRACTICEPLUMBINGEXAMS.COM
  4. 4.  The F&E cistern is located at the highest point in the system, it must not be affected by the position of the circulating pump or allow for over pumping  To avoid any problems with gravity primaries, a minimum height can be obtained by the following equation  The maximum head given by the pump ÷ 3  In a fully pumped system the level of water in the F&E cistern should be a minimum of 1 metre above the pumped primary to the hot-water storage cylinder.  No valves are to be on the feed or open vent This could have disastrous consequences if both are closed PRACTICE PLUMBING EXAMS © WWW.PRACTICEPLUMBINGEXAMS.COM
  5. 5. • The cistern and float valve must withstand temperatures of 100°C. The float valve must comply with (BS1212) • The system volume expands by around 4 % when heated. • How much would a system with 100 L of water expand by when heated ? ----------4L • This is why expansion + 25 mm must be allowed in the F&E cistern PRACTICE PLUMBING EXAMS © WWW.PRACTICEPLUMBINGEXAMS.COM
  6. 6. • This should rise to a minimum height of 450 mm above the water level in the F&E cistern to allow for any pressure surge created by the circulator pump. • The purpose of the primary open safety vent is to: • Allow for expansion in the event of over heating and allow the system to be open to atmospheric pressure. • There should be no valve on the open vent and should be a minimum of 22mm in diameter. PRACTICE PLUMBING EXAMS © WWW.PRACTICEPLUMBINGEXAMS.COM
  7. 7. • Air separators are used when the connection of the open vent pipe and the cold feed need to be close together to comply with the design of the system. • The air separator allows for air in the system to escape through the open vent making the system quieter. PRACTICE PLUMBING EXAMS © WWW.PRACTICEPLUMBINGEXAMS.COM
  8. 8. • Isolation valves must be fitted to both side of the pump to allow for servicing and maintenance. • Pumps contain a impeller which is turned by a motor circulating the water that's why pumps are relater to as impeller pumps or circulator pumps a • It is the pump’s job to circulate water around the central-heating system • Most pumps have three settings, the pump manufacturers provide performance data for each, which shows flow rate in litres per second and pressure in k Pa and m head. PRACTICE PLUMBING EXAMS © WWW.PRACTICEPLUMBINGEXAMS.COM
  10. 10.  Most pumps deliver 5 to 6 m head around 0.5 to 0.6 bar.  The flow rate on small bore systems should not be above 1 litter per second.  The flow rate on micro bore systems ( pipe work smaller than 15mm) should not deliver more than 1.5 letters per minute.  When positioning the pump you must make sure the pump provides a positive pressure to the system and does not allow for over pumping of the water through the open vent. PRACTICE PLUMBING EXAMS © WWW.PRACTICEPLUMBINGEXAMS.COM