Dwyer OP User Manual

Series OP Orifice Plate Flow Meter

Specifications - Installation and Operating Instructions

1/4˝ NPT PRESSURE FITTING

C

L

A

HI

ORIFICE PLATE

1/8 (3.18)

THICK TYPICAL

(CARRIER RING)

BODY

PRESSURE

4-1/2

OD

(114.3)

C

LOW

A

L

PRESSURE

INCLUDES RING GASKET

ADHERED TO FACES

Bulletin F-OP

ID

FLOW

1-1/4

(31.75)

The Series OP Orifice Plate Flow Meter is a complete orifice
plate flow metering package. It incorporates a stainless steel
orifice plate with a unique holder or carrier ring containing metering
taps and integral gaskets. It was designed for use wherever there
is an application for a conventional flow orifice plate. It can also be
used in place of other primary differential producers for efficiency
and cost effectiveness. Installation is accomplished simply by
slipping the unit between standard flanges (orifice flanges are not
required). The Series OP is available in line sizes from 1/2˝ to 24˝
and can be used with compatible liquids and gases.

ACCURACY

The Series OP utilizes the corner tap proportions as defined in ISO

5167. While this code may not be referred to as International
Standard until accepted by the ISO Council, the ASME Fluid
Meters Research Committee has suggested that the
dimensionless coefficient equation developed by the International
Standards Organization (ISO) and presented in ISO 5167 is
significantly better for the broad spectrum of flow measurement
applications throughout process industries.

The coefficient values used in the Series OP bore calculations
represent the same confidence level assigned to the flange and
radius taps widely accepted in fluid flow measurement.

The accuracy assigned to the coefficient values is ±0.6% full scale
flow for d/D (Beta) values 0.2 to 0.6 and ±0.7% for Beta values 0.7
to 0.75 (i.e. ß of 0.7 would have an uncertainty value of ±0.7% full
scale flow).

Accuracy of the differential signal produced by the Series OP
equals or exceeds that of a properly manufactured and installed
flange or radius tap orifice meter.

SPECIFICA T IONS
Service: For metering compatible liquids & gases.
Wetted Material: 304 SS, Buna-N gaskets.
Accuracy: 0.6% of full scale flow. (Beta = .2-.6) ±0.7% for Beta

greater than .6.

Temperature: -50 to 200°F (-45 to 93°C).
Pressure: Limited only by pipe and flange rating r estrictions.
Head Loss: 1-Beta ratio

2

eg: 1-0.72or 1-0.49 = 51% of the d.p.

Line Sizes: 1/2˝ to 24˝.
Process Connection: 1/4˝ female NPT .
Installation: Standard flange, any rating (orifice flanges not r equired).
Pipe Requirements: General requirements 10 diameter upstream

and 5 diameter downstream of orifice plate.

Weight: Varies with line size. See chart.

MOUNTING

The orifice metering primary shall be suitable for installation
between standard ANSI 125/150# flanges (any material) mounted
on standard pipe (any material). The unit shall be "self centering"
within the bolt circle of the flanges. No alignment of the orifice shall
be necessary unless used with 300# or non-standard flange
ratings. Drilling and or tapping of the main or flanges will not be
allowed or required. The overall laying length shall be 1.25˝
including pre-attached ring type 1/8˝ thick Buna "N" Gaskets.

Pipe Requirements: Upstream and downstream pipe
requirements are contingent upon two factors: (a) Beta Ratio-ratio
of the orifice bore to the pipe I.D. (d/D); (b) The type of fitting or
disturbance upstream of the Series OP. For most applications, 10
pipe dia. upstream & 5 dia. downstream are sufficient. (5 pipe dia.
up and 2 dia. down are acceptable for non-critical application.)

DWYER INSTRUMENTS, INC.

Phone: [phone] www.dwyer-inst.com

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46361, U.S.A. Fax: [phone] e-mail: [e-mail]

Installation Tips: (a) If possible, do not install a valve upstream if

it is going to be throttled. Install on the downstream a minimum of
6 diameters from the Series OP. (b) The use of straightening vanes
is not necessary for most applications.

Installation: (a) Insert bolts through bottom half of the flange bolt
circle. (b) Slide OP between flanges (make sure arrow on OP faces
in the direction of flow). (c) Make sure pressure connections are
properly positioned. For horizontal liquid lines, install the OP with
the connections on or under the horizontal center line. For
horizontal air or gas lines, install with the connections on or above
the horizontal center line. They should also be correctly oriented so
as to not be blocked by bolts when remainder of bolts are
inserted. (d) Add rest of bolts and nuts leaving all bolts loose so the
OP is free to move. (e) For non-standard flanges, the OP can be
centered using a steel ruler to measure the total side to side
movement and set OP at half way point all around. (f) Lubricate &
tighten bolts diametrically alternating to recommend flange torque.
(g) Check to insure the OP is installed with the arrow facing in the
same direction as flow. Flange bolts should be 1.25˝ longer than
standard flange bolts.

HEAD LOSS

FLOW vs. DIFFERENTIAL PRESSURE RELATIONSHIP
(Based on constant inlet temperature and pressure)

2

/ Q1]2x h1= h2Solve for new d.p. based on changes in flow

[Q

√

h2/h1x Q1= Q2Solve for new flow based on changes in d.p.

Where:

= Existing Flow

Q

1

= New Flow

Q

2

= Existing d.p.

h

1

h

= New d.p.

2

If the inlet temperature and pressure fluctuate, use the full formula
allowing for input of varying temperature and pressure.

To convert 60°F water flow rates for other fluids:
Pounds per hour (for any fluid) = Q x 63.3 x γ

√

L

To convert 60°F water flow rates into flow rates for gases:
Standard cu ft/hour (for any gas) = Q x 63.3 x (γL)/(γS)

√

To convert 60°F water flow rates to GPM for other fluids:
(GPM) / ( SG of fluid)

√

Explanation of Symbols
Q = 60°F Water Flow Rate in GPM
SG = Specific Gravity

γ

= Specific Weight of Line Fluid in lb/ft3at line conditions

L

γ

= Specific Weight of Line Fluid in lb/ft3at standard conditions

S

(60°F, 14.7 PSIA)

Overall Pressure Loss Across Thin-Plate Orifices

The above curved graph shows pressure loss generated by the
Series OP. For example, a 0.7 Beta Ratio (d/D) would show a loss
of 51%.

As a quick check reference, you can use the formula: Head loss
=1-Beta Ratio

Source: ASME Research Report on Fluid Meters

2

eg: 1-0.72or 1-0.49 = 51% of the d.p.

Magnehelic®and Capsuhelic®gages from Dwyer read pressure
drop across the orifice plates.

For compatible gases a Dwyer Magnehelic®gage may be used to
read the differential pressure. Compatible liquids may be used in
conjunction with the Dwyer Capsuhelic

®

gage with brass case.