EPS Leading meter2 Dual Chamber Orifice Fittings

What Is a Dual Chamber Orifice Fitting?

A dual chamber orifice fitting is an orifice plate carrier whose body contains two chambers that can be separated from each other. The lower chamber lies in the flow path and holds the plate concentrically during measurement. The upper chamber is the access section into which the plate is withdrawn for maintenance, and a sealing isolation valve separates it from the lower chamber. With this arrangement the plate can be moved into the upper chamber while the line is under pressure; the upper chamber is then isolated from the line and vented, and the plate can be taken out.

In single chamber fittings, a plate change requires the relevant line section to be isolated and depressurized. The dual chamber design removes this requirement: flow keeps passing through the fitting, and the station does not have to be shut down or switched to a bypass. For this reason dual chamber fittings are widely used at gas transmission and distribution stations where flow must continue without interruption, and at measuring points whose flow rate varies over time.

EPS Leading meter2 is a dual chamber fitting designed for ease of manufacture and assembly, with a reduced number of complex parts. Its modular design allows an installed meter1 single chamber fitting to be upgraded to meter2 while it remains in the line, and a double isolation option is available for plants that require proved double isolation.

Changing the Plate Under Pressure: How It Works

In a dual chamber fitting, a plate change is based on equalizing the upper chamber with line pressure and then separating it from the line. A typical change cycle consists of the following steps:

1.      Normal metering position: The plate sits in the lower chamber, perpendicular to the flow and concentric with the bore. The isolation valve is closed and the upper chamber is separated from the line. The differential pressure from the pressure tappings in the body is passed to the transmitter.

2.      Pressure equalization: Opening the equalizing valve brings the upper chamber up to line pressure. Once the pressures on both sides of the isolation valve are equal, the valve can be opened without damaging its sealing surfaces.

3.      Raising the plate into the upper chamber: The isolation valve is opened and the drive shafts draw the plate carrier up from the lower chamber into the upper chamber. Meanwhile, flow continues to pass through the bore of the fitting.

4.      Isolation and venting: The isolation valve and the equalizing valve are closed; the upper chamber is vented through the bleed valve to a safe location and zero pressure is confirmed.

5.      Removing and inspecting the plate: The top cover is opened and the plate is taken out; edge sharpness, flatness and bore diameter are checked, or a plate with a different bore is fitted. The quick-release plate system prevents the plate from being installed in the wrong orientation.

6.      Returning to the metering position: The cover and the bleed valve are closed, the upper chamber is equalized again, the isolation valve is opened so the plate can be lowered into the lower chamber, and the valve is closed. The plate bore is updated in the flow computer and metering resumes.

What Happens to the Measurement During a Plate Change?

Flow is not interrupted, but while the plate is in the upper chamber there is no restriction in the flow path, so no differential pressure is generated and flow cannot be calculated. For this short period the flow computer is put into maintenance mode and, according to the station's metering procedure, an estimated value or a backup measurement is used. Being able to change the plate quickly and predictably keeps this unmeasured interval short.

Modular Design: From Single to Dual Chamber

Within the EPS Leading fitting family, meter1 and meter2 share a modular construction. A station where a single chamber design is sufficient today can start with meter1; when operating needs change, the fitting can be upgraded to meter2 while it remains in the line. This adds uninterrupted maintenance capability without cutting or welding the pipeline and protects the existing investment.

Difference Between Dual Chamber and Double Isolation Designs

In a standard dual chamber fitting, the upper chamber is separated from the line by a single isolation valve. Some operators' isolation philosophies require isolation to be proved with two independent barriers and a bleed in between before a pressurized chamber may be opened. For such a requirement, the double isolation option of meter2, or the meter2di working on the double block and bleed (DBB) principle, should be considered.

Key Features

·         Plate change under pressure: The plate is raised into the upper chamber, inspected and changed while the line is pressurized; flow is not interrupted and no bypass is needed.

·         Modular design: An installed meter1 single chamber fitting can be upgraded to the meter2 dual chamber design while it stays in the line.

·         Reversal-proof quick-release plate system: The plate can only be placed in the carrier in the correct orientation, and the quick-release mechanism keeps plate changes in the upper chamber short.

·         Simple body with few parts: Designed around ease of manufacture and assembly (DFM/DFA), the body has fewer complex parts and uses modern sealing solutions.

·         Field-repairable construction: Seals and internal parts are accessible on site; the fitting does not have to be sent to a workshop.

·         Horizontal or vertical installation: meter2 is suitable for installation in horizontal or vertical lines.

·         FEA-verified dual chamber body: The body with its upper and lower chambers is verified by finite element analysis (FEA) at design stage; after assembly, every unit is pressure tested against European pressure guidelines and industrial safety requirements.

·         High-pressure solutions: In addition to the standard ANSI classes, high-pressure designs up to 10,000 psi can be assessed per project.

·         Double isolation option: A double isolation variant is available for operators that require proved double isolation.

·         Rationalized product range: The range has been streamlined with the aim of shortening lead times; the meter run and accessories can be supplied within the same scope.

Technical Specifications

The values below show the typical design scope of the meter2 dual chamber orifice fitting. The final configuration should be confirmed at project stage according to size, pressure class, material and connection type.

For the high pressure classes, body material and construction details are confirmed per project. Whether a given size / pressure class combination suits the selected line should be verified at quotation stage.

Key Advantages

·         Uninterrupted flow: Plate inspection and replacement do not require the station to be stopped or the flow to be switched to a bypass.

·         Maintenance independent of shutdown plans: Plate checks can be made whenever they are needed, without waiting for the annual maintenance shutdown.

·         Quick response to flow changes: When the flow range changes, switching quickly to a plate with a different beta ratio keeps the differential pressure within the transmitter's efficient operating band.

·         Modular upgrade that protects the investment: Stations that start with a single chamber fitting can move to dual chamber operation without modifying the pipeline.

·         Controlled, safe access: The plate is only reached after the upper chamber has been separated from the line and vented, so maintenance staff are not exposed to line pressure.

·         Protection against assembly errors: The reversal-proof plate system eliminates the risk of orientation errors during frequent plate changes.

·         Long service life: Stainless internals, seals selected for the application and a field-repairable design help keep the fitting in service for many years.

Application Areas

Dual chamber orifice fittings are used at measuring points where the plate must be reachable without stopping the flow.

Gas Transmission and Distribution Stations in Continuous Operation

At stations within the scope of ASME B31.8, plates can be inspected while gas keeps flowing, reducing the need for a standby meter run.

Measuring Points with Seasonal Flow Changes

On lines where flow differs markedly between summer and winter demand, the plate can be exchanged for one with a different beta ratio without stopping the flow, preserving the measuring range.

Process Plants

On continuously operating ASME B31.3 process lines, plates can be checked without a unit shutdown.

Power Plants

Can be applied as a flow measuring point on continuously operating lines covered by ASME B31.1 power piping.

High-Pressure and Sour Service

High-pressure solutions up to 10,000 psi, API 6A flange options and material selection in line with NACE MR0175 allow use under demanding service conditions.

Dual Chamber Orifice Fitting Selection Criteria

Besides pressure class and size, the plant's isolation rules are decisive when selecting a dual chamber fitting. The following information should be clarified for a technical assessment:

Maintenance and Isolation Requirements

·         Plate inspection and change frequency; seasonal variation of flow

·         The operator's isolation philosophy: is a single barrier sufficient, or is proved double block and bleed isolation required?

·         Lockout/tagout practices and procedures for maintenance staff

·         Flow computer maintenance mode and backup measurement approach during plate changes

Pressure Class and Nominal Size

·         Design pressure, and whether the selected ANSI class is offered in the required size

·         Need for a high-pressure (psi-rated) solution

·         Beta ratio range and the plate bores planned for different flow periods

Material and Seal Selection

·         Body casting suited to the minimum design temperature

·         Sour service or corrosive component content; internals material

·         Compatibility of the seal material with the fluid, temperature and pressure equalization cycles

·         External bolting coating and site corrosion conditions

Layout and Metering System

·         Horizontal or vertical installation; vertical maintenance clearance needed to remove the plate from the upper chamber

·         Need for a meter tube machined to suit the fitting and a flow conditioner

·         Scope of differential pressure, static pressure and temperature transmitters and flow computer

·         Upgrade potential of existing meter1 installations

Hazardous-area requirements for the electronic instruments connected to the fitting should be assessed per project according to the area classification of the station.

Design Codes, Isolation and Measurement Standards

The meter2 dual chamber orifice fitting is designed within the framework of the following standards, codes and guidance.

The compatibility of site-specific isolation procedures with the fitting design should be assessed at project stage together with the operator's safety team.

Dual Chamber Fitting Solutions from TLY Enerji

In dual chamber fitting projects, TLY Enerji takes the measuring point's need for uninterrupted operation and the plant's isolation rules as the starting point. We analyze your flow profile to prepare a plate bore plan for different periods, determine a suitable pressure class and material combination, and clarify with you whether a standard dual chamber design or a double isolation design is needed.

At existing stations we assess the upgrade potential of installed single chamber fittings; we define the meter run, transmitter and flow computer scope, handle technical documentation and control system integration, and work with your site teams during commissioning. We also help prepare field procedures that cover switching the flow computer to maintenance mode during plate changes.

Frequently Asked Questions

What is a dual chamber orifice fitting?

A dual chamber orifice fitting is a two-section orifice plate carrier: a metering chamber that holds the plate in the flow path, and an access chamber into which the plate is withdrawn for maintenance. A sealing isolation valve separates the two chambers. This construction allows the plate to be removed and inspected while the line is under pressure and without interrupting flow.

How is an orifice plate changed while the line is under pressure?

First the upper chamber is brought to line pressure with the equalizing valve and the isolation valve is opened. The drive shafts draw the plate into the upper chamber; the isolation valve is then closed and the upper chamber is vented through the bleed valve. Once zero pressure is confirmed, the top cover is opened and the plate removed. Refitting follows the same steps in reverse order.

Is metering interrupted during a plate change?

Flow is not interrupted, but while the plate is in the upper chamber no differential pressure is generated, so flow cannot be calculated. During this short period the flow computer is put into maintenance mode and an estimated value or backup measurement is used in line with the station procedure. The quick-release plate system and a simple change sequence help keep the unmeasured interval short.

Can an installed single chamber meter1 be upgraded to meter2?

Yes. The EPS Leading fitting family has a modular design, and an installed meter1 can be upgraded to the meter2 dual chamber design while it remains in the line. This adds the capability for uninterrupted plate changes without cutting or welding the pipeline. The feasibility of the upgrade should be confirmed by reviewing the size, pressure class and condition of the existing fitting.

What is the difference between a dual chamber and a double isolation fitting?

In meter2 there is a single sealing barrier between the chamber into which the plate is withdrawn and the line. A double isolation fitting has two independent barriers with a bleed point between them; the isolation is proved visibly with HP and LP pressure gauges and the valve shafts can be locked. Plants whose isolation philosophy requires double block and bleed should choose the double isolation design.

In which sizes and pressure classes is meter2 available?

meter2 is available in nominal sizes of 2–24 inch. The ANSI 150#–900# and 1500# classes are offered in all sizes, while the 2500# class is available from 2 to 12 inch. In addition, high-pressure solutions up to 10,000 psi can be assessed per project. The suitability of the chosen size and pressure class combination should be confirmed at quotation stage.

When should an orifice plate be changed?

The most common reason is a change in the flow range that takes the differential pressure outside the transmitter's efficient operating band; a plate with a different beta ratio is then fitted. Wear, nicks, bending or deposits on the plate edge found during periodic inspection also call for a change. A dual chamber fitting allows both tasks to be carried out without interrupting flow.

How is a dual chamber fitting maintained?

Routine maintenance covers tightness checks on the isolation, equalizing and bleed valves and the seals, confirmation that the drive shafts move freely, and plate inspection. meter2 is designed to be repaired in the field, and its seals are selected for the application. Maintenance intervals should be set according to fluid cleanliness, pressure cycling and plate change frequency.