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4.2.11. Installing Manifold Cylinders or Tanks. When installing manifold DOT cylinders or ASME tanks, it is essential to understand and identify the different components and applications required by safety codes for their installation. . In this module you will learn to:

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4.2.11

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4.2.11

Installing Manifold

Cylinders or Tanks

When installing manifold DOT cylinders or ASME tanks, it is essential to understand and identify the different components and applications required by safety codes for their installation.

  • In this module you will learn to:

  • Identify basic NFPA code requirements for manifold container installations

  • Identify manifold cylinder systems and applications

  • Select components for manifold cylinder systems

  • Identify components for typical vapor service manifold tank installations with single regulator configuration

  • Identify components for typical vapor service manifold tank installations with parallel regulator configuration

  • Identify code requirements and components for manifold tanks in liquid service


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NFPA Code Requirements for Manifold Container Installations


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NFPA Code Requirements for Manifold Container Installations


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NFPA Code Requirements for Manifold Container Installations


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Figure 2. 420-Pound

Stationary Cylinder

Figure 1. 100-Pound

Exchange Cylinders

Identifying Manifold Cylinder Systems and Applications

When two or more cylinders are connected, the vapor supply system is called a “manifold cylinder installation.” The cylinder filling method, and therefore, the type of cylinder used, generally determines the methods used for manifold cylinder connection, vapor flow control, and regulator selection.

Two basic manifold system types are:

  • Manual or automatic changeover systems, used with exchange cylinders

  • Dual cylinder manifold systems, used with stationary cylinders


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Identifying Manifold Cylinder Systems and Applications

Manual Changeover System— This manifold system relies on the customer to manually open and close the exchange cylinder service valves, or to switch over the valve in a connecting tee-block when the supply cylinder is empty and the reserve cylinder is needed.

Automatic Changeover System— This cylinder manifold uses a special two-stage regulator combining the first stage and second stage into one unit. Normally this regulator is connected to two cylinders or two banks of cylinders (Figure 3). When the pressure in the supply cylinder(s) drops to a low level, the regulator automatically switches over to the reserve cylinder(s) and does not interrupt the supply to the appliances.


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Figure 3. Automatic Changeover Regulator Manifold

Figure 4. Cross-Section View of Two-Stage Regulator with

Automatic Changeover, Service Pointer, and Service Indicator

Identifying Manifold Cylinder Systems and Applications


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Identifying Manifold Cylinder Systems and Applications

Dual Cylinder Manifold System— The cylinders of a stationary or dual cylinder installation are filled on site. Both cylinders usually supply propane to one regulator at the same time.

Figure 5. Dual Cylinder

Installation (Stationary Service)


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Selecting Components for Manifold Cylinder Systems

Service Valve Pigtails

Figure 6. Pigtails


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Figure 8. Manual

Changeover Tee

Figure 7. T-Check

Selecting T-Blocks for Manifold Cylinders

Manual Changeover Systems— The T-check is basically a T-block with a built-in floating check valve. When the empty supply cylinder is removed, the pressure in the full cylinder forces the check valve to slug shut. This allows the cylinder to be replaced without interrupting service to the appliances or discharging propane from the full cylinder.


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Figure 9. Automatic Changeover

(Low Capacity System)

Selecting Components for Manifold Cylinder Systems

Automatic Changeover System— For medium capacity systems (4 or 6 cylinders), assemble a manifold using POL T-block fittings and pigtails (Figure 9). One of the benefits of this type of arrangement is that additional cylinders can be connected to the assembly by simply adding POL T-blocks and pigtails.


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Figure 10b. POL T-Block Cutaway View

Figure 10a. POL T-Block

Figure 11a. POL T-Check

Figure 11b. POL T-Check Cutaway View

Selecting Components for Manifold Cylinder Systems


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Figure 12. Automatic Changeover

(High Capacity System)

Selecting Components for Manifold Cylinder Systems

For high capacity systems (above 750,000 Btu/hr) it is a good idea to use a rigid pipe manifold similar to the one illustrated in Figure 12. The supply manifold is assembled from 1/2" schedule 80 pipe and extra heavyweight pipe T's. Each cylinder is connected to a pipe T by a short pigtail. Each side of the manifold is connected to an inlet of the changeover regulator by an extra heavy-weight union and a short pipe nipple.


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Figure 13. Integral

2-Stage Regulator

Selecting a Cylinder Manifold Pressure Regulator

Pressure regulators for manifold cylinder installations must be a two-stage system and must meet the requirements of NFPA 58, LP-Gas Code, and UL 144 standard for LP-gas regulators.

The standards require sufficient excess pressure relief capacity to prevent gas pressure in excess of 2 psig from reaching the customer’s gas appliances, even in the event of failure of the first and second stage regulators in the full-open position.

Two factors must be considered when selecting the manifold system regulator:

  • Manifold system type

  • Total gas appliance demand in Btus per hour


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Figure 14. Automatic

Changeover (2-Stage)

Regulator

Selecting Components for Manifold Cylinder Systems

Regulators selected for cylinder manifold systems must have Btuh rating capacities in excess of the total gas appliance system load.


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Selecting Components for Manifold Abovground Systems

Figure 16. Excess-Flow POL Fitting

Figure 15. Manifold Aboveground ASME Tanks


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Selecting Components for Manifold Underground Systems

The loops in the copper tubing are used to provide flexibility for the tubing in the event of tank or regulator post movement due to settling or soil frost heave.

Figure 17. Manifold Underground ASME Tanks


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Figure 18. POL

Back Check Tee

Components for Manifold Vapor Service Tank Installations

with a Single Regulator

Underground manifold tank installation components:

  • Regulator vent pipe-away assembly

  • POL back check tee

  • Open-bottom water meter or valve box, or poured-in-place concrete vault with loose-fitting manhole cover


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Components for Manifold Vapor Service Tank Installations

with Parallel Regulators

Figure 19. Manifold ASME Tanks

& Parallel First-Stage Regulators


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Components for Manifold Vapor Service Tank Installations

with Parallel Regulators

The installation illustrated could use aboveground or underground ASME storage tanks.

If underground tanks are used, aboveground location of the regulator manifold is recommended.

Support for the regulator manifold should by provided by the use of a support post similar to the one used in the single regulator installation.

Figure 19. Manifold ASME Tanks

& Parallel First-Stage Regulators


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Figure 20. Excess- Flow

Angle Valve

Identifying Code Requirements and Components for Manifold Tanks in Liquid Service

If the actuated liquid withdrawal excess-flow valve (sometimes called an evacuation valve) is used for manifold tank connection, one of two forms of excess-flow protection must be provided:

  • A liquid transfer valve attached to an actuated liquid withdrawal excess-flow valve that is recommended by the manufacturer for continuous service, or

  • If the tank’s evacuation valve is not approved for continuous service:

  • The tank must be evacuated of liquid, and the vapor flared;

  • Tank vapor pressure reduced to atmospheric pressure;

  • The actuated liquid withdrawal excess-flow valve removed and replaced with a liquid transfer valve equipped with an internal excess-flow


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Figure 21. Internal Valve with Excess-Flow and Cutaway View

Identifying Code Requirements and Components for

Manifold Tanks in Liquid Service

If the bottom opening of the tank is used, it must be equipped with an internal excess-flow valve, and a manual shutoff valve installed as closed to the internal valve as possible.

The use of a close or “all-thread” pipe nipple to make the connection between the manual valve and excess-flow valve is not recommended.

In place of separate excess-flow and manual valves, a combined internal valve with excess-flow protection may be used. Internal valves of this type can be equipped with a remote closure feature.


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Figure 22.

Hydrostatic

Relief Valve

Figure 23. Stainless Steel Braided

Flexible Piping Section

Identifying Code Requirements and Components for

Manifold Tanks in Liquid Service

Liquid piping sections that can be closed at each end must be protected by the installation of a hydrostatic relief valve.

Hydrostatic relief valves should have a 400 to 450 psig start to discharge rating.

Liquid piping for manifold tanks is comprised of threaded schedule 80 pipe sections and heavy (2000 or 3000 pound) forged steel fittings.

Piping flexibility is provided by use of flexible sections.


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Figure 23. Stainless Steel Braided

Flexible Piping Section

Identifying Code Requirements and Components for

Manifold Tanks in Liquid Service

Flexible sections should never be used to make a turn or change in direction of piping runs.

They must be installed in a straight piping run, and must not be compressed or stretched. Use of a flex section that is too long will lead to failure of the stainless steel braids, distortion of the inner corrugated tube, and eventual rupture.


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Figure 24. Slab for Manifold Liquid Service Tanks

Identifying Code Requirements and Components for

Manifold Tanks in Liquid Service

Attaching vapor loads to tanks in liquid service is not recommended, especially if an auxiliary liquid pump set with a low-pressure switch and diaphragm-type bypass is not provided to feed liquid to the vaporizer.


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Time to See If You Got the Key Points of This Module…

  • Complete the Review on pages 15 - 17.

  • See if you are ready for the Certification Exam by checking off the performance criteria on pages 18 - 20.


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