1. Designing DOT Exchange and Stationary Cylinder Installations
4.1.3
Selecting an acceptable and appropriate location for the installation of DOT cylinders (exchange or stationary) is a very important decision in designing a propane distribution system. Ensuring the number and capacity of cylinders is critical to satisfactory system operation.
In this module you will learn to:
Identify regulations that govern cylinder location
Identify steps to finalize a cylinder location plan
Identify how to select DOT cylinders for vapor service
Identify requirements for locating manifold DOT cylinder systems
Select components for manifold DOT cylinder systems
Student Book  © 2004 Propane Education & Research Council
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2. Regulations that Govern Cylinder Location
DOT cylinders at customer installations shall be located no closer to ignition sources and building openings than the minimum distances set out in NFPA 58.
NFPA 58
2004
6.3
NFPA 58
2001
3.2.2
Figure 1. Minimum Distance Requirements for DOT/ICC Cylinder Installations
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3. Regulations that Govern Cylinder Location
Figure 1. Minimum Distance Requirements for DOT/ICC Cylinder Installations
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4. Regulations that Govern Cylinder Location
Figure 2. Distance Requirements for DOT Cylinders
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5. Steps to Finalize a Cylinder Location Plan
Explain to the customer the purpose in selecting a proper cylinder location.
Step 2:
Determine the customer’s general preference for the cylinder location (side of house, rear of house, etc.). Explain that the final location will have to meet safety regulations.
Step 3:
If the customer site has a limited distance to important buildings and property lines, select a location for the cylinders that has access for fuel delivery and fire fighting personnel.
Step 4:
If the cylinder is to be filled onsite (stationary cylinders), be sure there is access for fuel delivery from a bulk truck. Select a site that is no farther than 50’-60’ from the parking location for the bulk truck.
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6. Steps to Finalize a Cylinder Location Plan
Using a tape measure, select an area for the cylinder(s) that meets the distance requirements shown in Figure 2.
Step 6:
When the final location for the cylinder(s) has been selected, mark the location with a stake or flag.
Step 7:
Draw a simple sketch of the property and cylinder location on the worksheet. Indicate the total number and type of cylinders to be used. List any special tools or equipment that may be needed for the installation.
Step 8:
Point out and explain the choice of the cylinder location. If the customer is completely dissatisfied, try to find another location. Do not sacrifice or ignore any safety requirements for a location preferred by the customer. If another location cannot be found that meets all distance requirements, politely explain to the customer the reasons for the location.
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7. Sizing DOT Cylinders for Vapor Service
Factors Affecting the Vaporization Rate of Cylinders— When a cylinder(s) is sized for vapor service, make sure the vaporization rate of the cylinder(s), or withdrawal rate, is equal to or greater than the demand for propane.
Outside Surface Area of the Cylinder: The heat required to vaporize liquid is transferred through the walls of the cylinder. If the area of the cylinder which is in contact with the propane liquid (wetted surface area) is large, the total heat (Btu) that can be transferred to the liquid is high.
Level of Liquid Propane in the Cylinder
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8. Sizing DOT Cylinders for Vapor Service
Factors Affecting the Vaporization Rate of Cylinders—
Air Temperature Surrounding the Cylinder : High summer temperatures surrounding the cylinder create more available heat to be transferred to the liquid. As a result, the rate of vaporization is high. However, low outside temperatures in the winter reduce the cylinder vaporization capacity.
Relative Humidity: If the air is moist (high humidity), the air may cool down to a temperature where the moisture will condense on the wetted surface area of the cylinder & freeze. The resulting "frost line" on the wetted surface acts as an insulator and drastically reduces the vaporization rate of the cylinder.
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9. Sizing DOT Cylinders for Vapor Service
Procedures for Sizing Cylinders for Vapor Withdrawal —
Step 1:
Determine the total demand of all present and anticipated future appliances.
Locate the data or rating plate on each appliance in the system.
Record the input rating (Btu/hr.) of each appliance.
Add the input ratings for all existing appliances and the estimated input ratings for any future appliances to obtain the total vapor distribution system demand.
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10. Sizing DOT Cylinders for Vapor Service
Figure 3. Average Appliance Input Ratings and Load Factors
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11. Sizing DOT Cylinders for Vapor Service
Procedures for Sizing Cylinders for Vapor Withdrawal —
Step 2:
Determine the actual or effective load on the cylinder.
Determine the load factor for each gas appliance.
Determine the actual or effective load of each appliance.
Determine the total effective load on the cylinder.
Step 3:
Determine the most severe weather conditions under which the cylinder(s) must operate. The two most important factors affecting the vaporization rate of a propane cylinder are the temperature and the humidity of the air surrounding the cylinder.
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12. Sizing DOT Cylinders for Vapor Service
Procedures for Sizing Cylinders for Vapor Withdrawal —
Step 3:
Determine the most severe weather conditions under which the cylinder(s) must operate.
Determine the normal operating period under which the cylinder will provide propane vapor to appliances.
Determine the lowest anticipated outside temperature that will occur during the normal operating period, then select the appropriate temperature from the sizing table (Figure 5).
Determine the highest humidity that will occur during the normal operating season.
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13. Sizing DOT Cylinders for Vapor Service
Procedures for Sizing Cylinders for Vapor Withdrawal —
Figure 4. Humidity Map
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14. Figure 5. Vaporization Rate of Common DOT Cylinders
Sizing DOT Cylinders for Vapor Service
Procedures for Sizing Cylinders for Vapor Withdrawal —
Step 4:
Refer to the cylinder sizing table.
Figure 5. Vaporization Rate of Common DOT Cylinders
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15. Sizing DOT Cylinders for Vapor Service
Procedures for Sizing Cylinders for Vapor Withdrawal —
Step 5:
Select the proper size and number of propane cylinders for the installation.
The ratings are calculated when the liquid level is 25% of the water capacity of the cylinder or 1/4 full.
This factor in the sizing method assumes that cylinders will be exchanged or filled before they contain less than 25% propane liquid.
If the cylinder is 1/3 full, multiply by 1.144, etc.
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16. Sizing DOT Cylinders for Vapor Service
Sizing DOT Cylinders — Perform the following steps to select a DOT cylinder for a specific application:
Step 1:
Select the column in the table that represents the most severe weather conditions for the area.
Step 2:
Determine the type of cylinder needed.
Step 3:
Read down the column until a Btuh rating is located that equals or is greater than the effective load of the application.
Step 4:
Read straight across to the extreme left column and select the cylinder listed.
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17. Sizing DOT Cylinders for Vapor Service
When the effective load of the application is greater than the vaporization rate of either of the exchange cylinders listed in the table, two or more supply cylinders may be manifolded together.
Exchange 60 lb. and 100 lb. propane capacity cylinders are commonly installed in pairs, one reserve and one supply. As illustrated in Figure 6, one reserve cylinder must be added to the system for every additional supply cylinder. If the pressure in the supply cylinders drops too low, the automatic changeover regulator automatically changes over to the reserve cylinders.
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18. Sizing DOT Cylinders for Vapor Service
Figure 6. Exchange Cylinders in Service
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19. Cylinder Location Requirements
Because cylinders have water gallon capacities of less than 125 gallons, they may be installed alongside exterior building walls. However, if the aggregate water gallon capacity of the cylinders exceeds 501 gallons, they cannot be installed adjacent to building walls, as shown in Figure 7.
If groups of more than one manifold cylinders with aggregate capacity in excess of 501 water gallons are installed, the groups of manifold cylinders must be separated from each other or any other propane container by a distance of at least 25 feet.
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20. Cylinder Location Requirements
Figure 7. Maximum Number of Cylinders Permitted to be Installed Adjacent to Buildings
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21. Selecting Manifold Cylinder System Components
Identifying Manifold Cylinder Systems and Applications— When two or more cylinders are connected, the vapor supply system is called a “manifold cylinder installation.”
Figure Pound Exchange Cylinders
Figure Pound Stationary Cylinder
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22. Selecting Manifold Cylinder System Components
Three basic manifold system types are:
Manual changeover systems, used with exchange cylinders
Automatic changeover systems, used with exchange cylinders
Dual cylinder manifold systems, used with stationary cylinders
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23. Selecting Manifold Cylinder System Components
Figure 11. Cross-Section View of Two-Stage Regulator with Automatic Changeover, Service Pointer, and Service Indicator
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24. Selecting Manifold Cylinder System Components
Figure 12. Dual Cylinder Installation (Stationary Service)
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25. Selecting Manifold Cylinder System Components
Service Valve Pigtails
Figure 13. Pigtails
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26. Figure 16. Manual Changeover Tee
Selecting Manifold Cylinder System Components
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.
Figure 16. Manual Changeover Tee
Figure 14. T-Block
Figure 15. T-Check
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27. Selecting Manifold Cylinder System Components
Automatic Changeover System — For medium capacity systems (4 or 6 cylinders), assemble a manifold using POL T-block fittings and pigtails (Figure 17). 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.
Figures 18a & b. POL Tee Blocks
Figure 17. Automatic Changeover (Low Capacity System)
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28. Figure 19b. POL T-Check Cutaway View
Selecting Manifold Cylinder System Components
Figure 19a. POL T-Check
Figure 19b. POL T-Check Cutaway View
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29. Selecting Manifold Cylinder System Components
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 20.
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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30. Figure 20. Automatic Changeover (High Capacity System)
Selecting Manifold Cylinder System Components
Figure 20. Automatic Changeover (High Capacity System)
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31. Selecting Manifold Cylinder System Components
Selecting a Manifold Cylinder 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.
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32. Figure 21. Integral 2-Stage Regulator
Selecting Manifold Cylinder System Components
Manifold System Type — For dual stationary cylinder and manual changeover exchange cylinder manifold systems, an integral 2-stage regulator (Figure 21) is suitable for appliance loads of up to 500,000 Btuh, and relatively short piping runs.
Figure 21. Integral 2-Stage Regulator
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33. Figure 22. Automatic Changeover
Selecting Manifold Cylinder System Components
Manifold exchange cylinders in automatic changeover service require the use of two-stage regulator assemblies that include an automatic changeover valve and service indicator unit mounted before the first stage regulator.
Figure 22. Automatic Changeover
(2-Stage) Regulator
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34. Selecting Manifold Cylinder System Components
When selecting the regulator for a customer installation:
Determine each gas appliance input rating in the vapor distribution system and add them to obtain total gas appliance demand.
Consult regulator manufacturer specifications and maximum Btuh output capacity charts, or contact LP-gas equipment suppliers for assistance. Refer to the conditions that apply to the stated regulator output capacity, such as, “Rated output capacity based on input gas pressure of at least 100 psi.”
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35. Time to See If You Got the Key Points of This Module…
Complete the Review on pages
See if you are ready for the Certification Exam by checking off the performance criteria on pages 24 & 25.
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