Orifice Plates and Venturis

ORIFICE PLATES & VENTURIS Built to the recommendations of ASA, ISA, ASME and ISO Concentric, Eccentric, Quadrant edge, Bore with Counter bore and Segmental Plates are made in 304 and 316 SST, Monel, Hastelloy C and B, Alloy 20 and Teflon

ORIFICE PLATES

The orifice meter consists of a flat orifice plate with a circular hole drilled in it. There is a pressure tap upstream from the orifice plate and another just downstream. There are in general three methods of placing the taps. The coefficient of the meter depends upon the position of taps.

• Vena contracta location – Tap location 1 pipe diameter (actual inside) upstream and 0.3 to 0.8 pipe diameter downstream from face of orifice
• Flange location – Tap location 1 inch upstream and 1 inch downstream from face of orifice
• The orifice meter is recommended for clean and dirty liquids and some slurry services
• The rangeability is 4 to 1
• The pressure loss is medium
• Typical accuracy is 2-4% of full scale
• The required upstream diameter is 10 to 30
• The viscosity effect is high
• The relative cost is low

VENTURI FLOW ELEMENTS

• 1/4”-6 Line Sizes
• Low Unrecoverable Pressure loss
• Suitable for High Pressure
• Corrosive / Caustic Application
• Cryogenics or High Temperature

As the process approaches the contracted portion (throat) of the venturi flowmeter, the velocity of the process must increase as it flows through the contracted zone (throat).

The angle of approach is such that no turbulence is introduced into the stream. A pressure tap is located at the side wall in the pipe ahead of the meter and another one is located at the throat. The increase in velocity of the process through the throat results in a lower pressure at the throat.

The flow rate is proportional to the difference in pressure between the two taps. The gradual tapering of the meter walls back to pipe size downstream of the throat allows the process to slow down with a minimum of lost energy. This allows a recovery of nearly 99 percent of the pressure on the approach side. To monitor the amount of flow through the venturi flowmeter, a differential pressure gage is used to monitor the pressure difference between the two pressure taps.