Fives North American Combustion, Inc., 4455 East 71st Street, Cleveland, OH 44105 USA, Phone 216.271.6000
Fax 216.641.7852 email: fna.sales@fivesgroup.com • www.fivesgroup.com/fivesna
8695 ORIFICE PLATE
Data Sheet
Printed in USA
Page 3
Feb 2009
Orifice Installation Instructions
1. Plate Installation: Always handle orifice plates with care. A bend or damage to the internal bore or upstream face can create
measurement errors. Orifice plates have data stamped on the handle for easy identification. The orifice plate is to be installed and
secured in place between two flanges. Flange gaskets are to be used. The plate outside diameter is sized to fit within the flanges bolt
circle with all bolts installed. Care must be taken during installation so that the orifice bore is centered and as concentric as possible
with the pipe centerline.
2. Upstream Face: Beveled orifice plates need to be installed with the upstream face in the correct orientation relative to the
direction of flow (see figure 1). The sharp edge of the bore is the upstream face. The beveled edge is the downstream face.
“Upstream Face” will be stamped on the upstream face of the tang. Normal plate thickness for pipe sizes up to 14” will be 1/8”. Normal
plate thickness for pipe sizes 16” and larger will be ¼”. Certain applications with high differential pressures may require a thicker than
normal plate to prevent plate distortion. If the plate material thickness exceeds the calculated maximum allowable plate thickness, the
bore will be beveled. Plates that are not beveled are considered bidirectional.
3. Types of Pressure Tappings: Standard pressure tap locations shall be used. Follow the specified tap location dimensions
precisely. Install only the type of pressure tappings that correspond with the each orifice plate calculation. Orifice plates can be
calculated for Flange tappings, D and D/2 tappings or Corner tappings. Specific orifice flange assemblies can be supplied with
standard flange tappings (see figure 1) or standard corner tappings (not shown in fig. 1). For orifice plates without tappings in the
flange, D and D/2 tappings shall be used. D and D/2 tappings cannot be used for pipe sizes of 1-1/2” and under. Dimensional
limitations due to flange thickness may prevent the use of D and D/2 tappings on some larger pipe sizes. Vena contracta tappings are
not addressed or used in International Standard ISO 5167-1 &-2.
4. Flange Installation: For the most accurate and very precise measurements, weld neck flanges should be used. If slip on flanges
are used, the inside face of the pipe should be flush with, or as close as possible to the machined face of flange (some welding
standards requirements may not accommodate this). If screwed flanges are used, the pipe threads will not allow the pipe to be flush
with the machined face of the flange. The use of screwed and slip on flanges can create an unknown % of error but have worked
satisfactorily for most ratio control systems. The pipe or weld should never extend beyond the machined face of the flange. Assure
the flange gaskets do not extend inside the pipe line.
5. Pressure Tap Installation: Tappings should be oriented or installed on top or side of pipe to avoid moisture or dirt accumulating
in them. ½” npt tap connections are typically used for tappings. A half coupling should be welded to the pipe for D and D/2 tappings.
After installing couplings or after welding pipe to flanges with flange taps, carefully drill through the tap connections, drilling through the
pipe. The actual diameter of the drilled pressure tap holes at inner surface of pipe should not exceed: ¼” for 2-1/2” pipe and smaller;
3/8” for 3” pipe; ½” for pipes 4” and over. Remove all burrs from drilled holes; smooth the inside surface of the pipe around the drilled
holes; clean all chips from pipe and tap connections.
6. Straight Pipe Run Requirements: The minimum straight lengths required are the lengths between various fittings located
upstream or downstream of the orifice plate itself. Additional uncertainty or loss of accuracy cannot be predicted when straight lengths
are shorter than the values listed in table 1 (values expressed as multiples of internal diameter, D). It is recommended that control
valves are located downstream of the orifice plate. The valve listed in Table 1 assumes it is a full bore valve and is in the wide open
position. Per Table 1, straight lengths to be measured from the downstream end of the curved portion of the nearest (or only) bend, or
of the tee, or the downstream end of the curved or conical portion of the reducer or expander. The bends on which the lengths in this
table are based on had a radius of curvature equal to 1.5D. Column A for each fitting gives lengths corresponding to "zero additional
uncertainty" values. Column B for each fitting gives lengths corresponding to "0.5% additional uncertainty" values. Values are based
on International Standard Table 3-ISO 5167-2:2003(E) and are for reference only. For more precise measurement or for other fittings
and the limitations of the separation between the two bends and appropriate lengths of reducers and expanders see the ISO 5167-2
standard. A flow conditioner will permit the use of shorter upstream pipe runs.
Upstream (inlet) side of orifice plate
β ratio
Single 90
degree bend.
Two 90 degree
bends in the
same plane.
Single 90
degree tee
with or with
out extension.
Single 45
degree bend.
Full bore ball
valve.
Concentric
reducer
Concentric
Expander
Abrupt
symmetrical
reduction.
Down-stream
(outlet) side
d/D
Two 90 degree
bends in any
plane.
Mitre 90
degree bend.
Two 45 degree
bends in the
same plane.
Gate valve
fully open.
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
<=0.20
6
3
10
10
3
3
7
7
12
6
5
5
6
6
30
15
4
2
0.40
16
3
10
10
9
3
30
9
12
6
5
5
12
8
30
15
6
3
0.50
22
9
18
10
19
9
30
18
12
6
8
5
20
9
30
15
6
3
0.60
42
13
30
18
29
18
30
18
14
7
9
5
26
11
30
15
7
3.5
0.67
44
20
44
18
36
18
44
18
18
9
12
6
28
14
30
15
7
3.5
0.75
44
20
44
18
44
18
44
18
24
12
13
8
36
18
30
15
8
4
Table 1
