I. Introduction
The goal of the installation process is to install a valve with the least amount of torque or tightness that will make a leak-tight seal that lasts throughout the use of the valve-cylinder assembly. This Luxfer Technical Bulletin give torques that should not be exceeded during installation of straight-thread valves of US thread designs and provides information about O-rings and leak-tight seals. Some installation torque values for selected non-US thread designs (commonly used in the USA and North American) are also included in this bulletin.
Installing valves into high-pressure aluminum alloy cylinders and composite cylinders with aluminum alloy liners varies depending on the following factors:
- Type of valve
- Valve threading
- Lubricant (if used) and lubricant quantity
- Valve material
- O-ring specifications (i.e., type, material, size, shape, etc.)
- Cylinder material
Most Luxfer cylinders manufactured in the USA have threads that meet North American thread standards, dimensions and features of which differ from European and international threads.
Valve installation guidelines are given in CGA V-11, General Guidelines for the Installation of Valves into High Pressure Aluminum Alloy Cylinders. Please follow these CGA guidelines when writing procedures for valve installation and include inspecting valves and O-rings prior to installing valves into aluminum alloy cylinders and liners.
Luxfer does not recommend any particular valve manufacturer. While the choice of valve manufacturer is up to the filler, user or purchaser, the valve chosen must be compatible and suitable for the particular gas service and pressure. However, Luxfer does recommend that any valve chosen meet either a national or international valve standard current at the time the valve was manufactured (e.g., CGA V-9 or ISO 10297).
This bulletin contains recommendations only for brass valves with nickel coating. Other valve materials and designs are not covered.
As valve and cylinder threads age, they may become damaged or altered due to wear and previous improper insertion. Recommendations for old, previously used valves and old cylinders will necessarily differ from recommendations for new valves and cylinders. Since Luxfer has no knowledge of how used valves have been treated, Luxfer provides no guidance for installing used valves into new or old cylinders and no guidance for installing new valves into old cylinders.
Recommendations for torque and tightness vary depending on whether lubricants (defined in CGA V-11) are used or not. Tightness required to achieve a leak-tight seal depends on whether a lubricant is used and, if so, the quantity applied. Luxfer straight-thread cylinders require no lubricant for proper valve installation.
New straight-thread, nickel-plated brass valves can be tightened to within a given torque range into new Luxfer aluminum alloy cylinders or composite cylinders with aluminum alloy liners. The seal is made at the O-ring. Using the correct O-ring specification (i.e., type, material, size, shape, etc.) is very important to achieve a leak-tight seal; the O-ring material must be compatible with valve materials and the gas, and it must perform properly in the sealing process. Exact O-ring dimensions are also very important to make a proper seal. Use only the correct O-ring, and do not substitute other types of gaskets or O-rings. Luxfer’s torque recommendations are only for a straight-thread valve using an O-ring made of PTFE material. (O-rings made of other materials may require different torque limits not covered in this bulletin.) Do not reuse an O-ring if it is made from a material that permanently deforms when used (e.g., Buta N). Use a new O-ring when the old one is of the kind that deforms when used.
Tapered-thread valves are commonly lubricated using PTFE tape; CGA V-11 also lists other acceptable lubricants. Tapered threads form a seal in the threaded area. Lubricant type and quantity (including tape dimensions) affect the leak-tightness of a seal. Because distortion of valve and/or cylinder threads in used valves and cylinders can alter a leak-tight seal, Luxfer does not provide guidelines for inserting used valves into new or old cylinders or new valves into old cylinders.
A proper valve installation occurs when the minimum tightness is used to make a leak-tight, valve-to-cylinder seal that will last throughout the life of the valve-cylinder assembly or until the valve is removed. Do not over-tighten valves! Over-tightening can damage both valves and cylinders and may lead to unsafe situations that can cause property damage, injury and/or loss of life.
This bulletin covers the recommended maximum torque values for inserting new non-lubricated nickel-plated brass valves into new, US-designed straight-thread Luxfer aluminum alloy cylinders and Luxfer composite cylinders with aluminum alloy liners, both fitted with PTFE O-rings. Also included are some torque values for common international thread designs.
II. Exceptions
If the type of valve, valve material or thread dimensions do not match assumptions and specifications given above or dimensions in tables below, then Luxfer US provides no recommendations.
Moreover, if the valve and cylinder are components in another assembled product, Luxfer recommendations do not apply. In this case, consult the product assembler/manufacturer for valve insertion instructions and recommended torques.
For valves and valve dimensions not covered in CGA V-11, consult the valve manufacturer for installation guidelines.
Thread designs not of US design (e.g., UN, ISO, European, etc.) should follow installation guidelines and recommended torque values of the relevant standard(s) and/or values recommended by valve manufacturers of those thread designs. A few commonly used non-US-designed thread types are included in this bulletin.
III. Straight-thread valve installation and torque
Follow installation guidelines in CGA V-11. Use proper tools to guarantee proper installation. The following maximum torque values in Table 1 are given for installing new, non-lubricated nickel-coated brass straight-thread valves with PTFE O-rings into new Luxfer aluminum alloy cylinders and Luxfer composite cylinders with aluminum alloy liners (Section I assumptions and specifications apply). Use minimum torque values to make a leak-tight seal that will last throughout the use of the assembly.
NOTE: Thread designations that are even numbers (e.g., 18, 14, 16, etc.) are straight- thread designs. Thread designations with odd number designations are taper-thread designs.
TABLE 1
Maximum torque for North American new, straight-thread brass valves installed into new Luxfer aluminum alloy cylinders and composite cylinder liners—use the least possible torque to make a leak-tight seal
Straight-thread dimension Torque not to exceed
.625 – 18 UNF 50 lbf-ft (67.7 Nm)
.750 - 14 NGS 100 lbf-ft (135.58 Nm)
.750 - 16 UNF 75 lbf-ft (101.7 Nm)
.875 – 14 UNF 80 lbf-ft (108.46 Nm)
1.125 – 12 UNF 100 lbf-ft (135.58 Nm)
IV. Taper-thread valve installation
Follow pre-installation guidelines and installation/insertion guidelines given in CGA V-11. In North America, installation of taper-thread valves into taper-thread cylinders is not done by torque; accordingly, Luxfer does not provide torque values for such valves.
However, international and some European taper-thread valve types can be installed up to a given maximum torque provided that excess lubrication is avoided and Section I assumptions and specifications are followed; these torque values are given in Table 2. Use minimum torque values to make a leak-tight seal.
TABLE 2
Maximum torque values for installing new, nickel-plated brass valves into new Luxfer aluminum alloy cylinders and composite cylinder liners of non-North American design
Taper-thread dimension Final torque not to exceed
17E 70 lbf-ft (95 N m)
25E 81 lbf-ft (110 Nm)
Straight-thread dimension Final torque not to exceed
M18 x 1.5 6H 74 lbf-ft (100 Nm)
IV Special considerations
A. Oxygen
When cylinders and valves are used in oxygen service in which oxygen content exceeds 23.5% by volume, special cleaning and preparation of both the cylinder and valve are required. Cleanliness requirements are contained in industry standards and regulations. Valves must not be lubricated with any material (e.g., hydrocarbons, oils, gels, etc.) that may contribute to a fire, in this service.
B. Oxidizing gases
Like oxygen, oxidizing gases (e.g., nitrous oxide, N2O) require special valve and cylinder cleaning and preparation. Other types of oxidizing gases may require special valves. Seek guidance from the filler or gas supplier to determine the proper valve to be used with a particular gas. Valves must not be lubricated with any material (e.g., hydrocarbons, oils, gels, etc.) that may contribute to a fire, in this service.
C. Other
Follow CGA V-11 for writing valve installation procedures for valves and valve-cylinder configurations not covered in this Luxfer Technical Bulletin, or contact the valve manufacturer for guidance.
V Summary
Use the proper valve and cylinder for the intended gas and pressure as specified in Transport Canada regulations and US Department of Transportation (DOT) regulations. Follow guidelines in CGA V-11 for writing valve installation procedures. Follow those procedures consistently. Follow the valve manufacturer’s guidelines for the care, handling and inspection of valves. Luxfer recommends that only valves verified as having been made to a recognized standard (published by CGA, a regulatory authority or international standards body) be installed into Luxfer aluminum alloy cylinders and liners. Lastly, fillers should follow pre-fill equipment checks and after-fill equipment checks required by regulations and/or recommended by the CGA and standards bodies.
March 2011