Metering Stations (frequently referred to as Orifice Plates) are used to measure the flowrate in water distribution systems in HVAC heating and chilled water circuits, typically in commercial buildings such as hotels, offices and shopping malls and municipal buildings such as hospitals, airports, schools and government buildings.
Metering stations can be installed individually to measure flowrate in a system or coupled to a regulating or balancing valve to create a ‘Commissioning Set’. This allows flow regulation and the measurement of flowrate from a single location.
The Orifice plate metering stations consist of a wafer style stainless steel body with an integral precision machined orifice. Two Test Points (also known as P/T plugs) are fitted to the Metering Station body, one each upstream and downstream of the orifice. By measuring the pressure at each test point, the ∆p (or signal) across the orifice can be determined. The flow rate corresponding to the ∆p can be read from the flow graphs provided.
Installation of the Metering Station is very simple. It is mounted between two pipeline flanges with the body generally centralised by the bolt circle of the flange bolts. In order to make the test points accessible to the commissioning engineer, two stainless steel extension pieces are provided which are screwed into the Metering Station body and the test points are then fitted to the extensions. This feature also allows for insulation material to be applied, for example in chilled water systems and still allow access to the test points.
Metering stations should be installed in straight pipe runs to avoid disturbance of the flow profile. Local installation conditions will determine what is practically achievable but 5D (5 pipe diameters) upstream and 2D downstream of straight pipe with no interruptions should be regarded as the minimum which will typically provide an accuracy of flow measurement to within ±5% of design flow rate.
Some Key Facts
- Manufactured in 304 grade Stainless Steel, (316 grade Stainless Steel and Aluminium Bronze are also available).
- Stainless steel integral body and orifice.
- Standard size range DN50 to DN900 with larger sizes up to DN1500 also available to order.
- Designed in accordance with BS1042.
- Flow characteristics confirmed to BS7350.
- Flow measurement accuracy to within +/- 5% of design flow rate.
- Wafer pattern design suitable for installation within flange bolting to BS EN 1092-1 PN16.
- Designs also available to suit PN25, PN40, ANSI Classes 150 and 300.
- Can be close coupled to oblique globe type balancing valves complying with BS7350 (up to DN300).
- Self-sealing pressure test points.
- Lifting eyebolt supplied on sizes DN450 and larger.
- Flow charts and full installation instructions are available.