This valve allows
the cylinder to contain gases and allows gas to
be filled into or emptied from the cylinder. The
cylinder valve is the most vulnerable part of the
compressed gas package and requires a thorough
understanding to maximize its performance. There
are three basic valves used in the compressed
gas industry: the pressure seal valve, the packed
valve, and the diaphragm valve. There are sev
eral versions or designs within each of the three
basic types. This pamphlet will address the more
common valves in todays industry.
A working knowledge of cylinder valves can
improve processes, save time and money, prevent
problems, and improve the safety of your opera
tion. This document must not be used as a guide
for valve modification or repair. No modifications to
valves are permitted and any repairs shall only be
made by or under direction of the supplier.
Table 1
Basic Valve Rules
Always
open valves slowly to control pressure surges and
heat of compression!
use the correct CGA connection for hookup!
inspect the valve for damage and foreign
materials before connecting it to your equipment!
ensure when the cylinder is not in use, even when
empty, that the valve is in the closed position with
the outlet seal in place and the transport cap is
installed!
consult your supplier if you have any questions
regarding cylinder valves!
make packing nut adjustments with the valve
outlet depressurized!
restrain cylinders!
Important
When returning any cylinder, ensure that the cylinder
valve is properly closed, any outlet seals are in place and
properly tightened, and the transport cap is correctly
installed.


Never
tamper with pressure relief devices!
attempt to tighten or loosen the valve into or out
of the cylinder!
use a damaged valve where integrity may have
been affected!
continue to use a valve that operates abnormally,
i.e., becomes noisy or progressively harder
to operate!
use an automatic operator, adapter, wrenches, or
other tools to obtain a mechanical advantage on
handwheeloperated valves without consulting
your supplier first!
lubricate valves or their connections!
drag, lift, or move a cylinder using the valve or the
handwheel as a handle!
remove packing nuts on packed valves!
adjust or tamper with retainer or bonnet nuts on
diaphragm or pressure seal valves!
use the cylinder valve to regulate flow or pressure!
move cylinders without the transport cap installed!
interchange transport caps between cylinders! Figure 1
Pressure Seal Valve
Figure 2
Wrench-Operated Packed Valve
Spring Assembly
Handwheel
Bonnet
Packing
Upper Stem
Lower Stem
Pressure Relief Device
Seat Insert
Valve Body
Valve Stem
Packing Nut
Packing Follower
Packing
Valve Body
Valve Seat
Pressure Relief Device
Pressure Seal Valve (Figure 1)
Products: Inerts, Oxygen, Hydrogen
Operating Principle: The pressure seal valve is
a handwheeloperated valve using a twopiece
valve stem. The upper and lower stems interface
with either a key arrangement or a slot and blade
configuration. The threads are located on the lower
stem, and the upper stem is freefloating. A Teflon
®

material packing ring that makes contact with a
ridge on the upper stem provides the seal around
the valve stem. The force that provides this contact
is a spring located in the handwheel. This spring
provides an upward force to the upper stem and
pulls the stems sealing ridge into the packing ring.
Identifying Features
1. A spring in the handwheel can be detected by
wiggling the handwheel. If a spring is present,
the handwheel will pivot on the spring.
2. The valve has a nonrising handwheel. The
handwheel is always in the same position
relative to the valve body, regardless of whether
the valve is in the open or closed position.
Recommended Opening Procedure: Air Products
recommends pressure seal valves be used in the
fully open or backseated position. Opening the
valve fully causes the lower stem to ride upward
on its threads until it contacts the upper stem
and mechanically drives the upper stems seal
ridge into the packing ring. This improves the seal
around the stem and helps to prevent packing
leaks. Valves in the backseated position can be
mistaken as closed by inexperienced or untrained
operators. When an operator checks a valve to
ensure its position, he should always check by
attempting to close the valve, never by trying to
open the valve. If the valve was backseated using
substantial effort, it is possible that the operator
could think the valve is closed, when in fact it is
fully open. Operators must be trained to use pres
sure readings or an equally reliable indicator to
ensure that the cylinder valve is closed or open.
Recommended Closing Procedure: Close
the cylinder valve tightly using a gloved hand.
Air Products recommends always wearing gloves
when operating cylinder valves. NEVER use
wrenches or other persuaders to operate the valve.
Valve Advantages: The pressure seal valve is
extremely reliable, very strong (used at pressures
up to 6000 psig), economical, and userfriendly.
Valve Disadvantages: The valve is prone to leak
age around the stem, especially inboard leakage
when a vacuum is pulled on the valve outlet.
Backseating helps minimize outboard leakage
when the valve is in the open position. The threads
on the lower valve stem are in the wetted gas
stream. These threads are lubricated, and these
lubricants can be an unwanted contaminant in
highpurity applications.
Comments: This is a very reliable valve for non
corrosive and highpurity products. However, the
design makes this valve inappropriate for corro
sives and ultrahighpurity products.
The Wrench-Operated Packed
Valve (Figure 2)
Products: Corrosives and Reactive Gases
Operating Principle: The wrenchoperated valve
is a packed valve with a onepiece stem. The seat
tostem seal is a metaltometal seal. The manu
facturers minimum recommended closing torque
is 35 ftlbs. This is much more than can be applied
with hand force; therefore, the valve requires a
wrench to provide sufficient closing force. The
stem seal is accomplished by compressing a large
ring of Teflon material between the valve body and
packing nut, which forces the Teflon material to
grip the stem.
Identifying Features
1. The valve does not have a handwheel. The top
of the stem is machined square to accommo
date a wrench.
2. The top of the valve has a large, internal
threaded nut screwed onto the body, where the
valves stem exits. This is the packing nut.
Recommended Opening Procedure: The wrench
operated valve has a very large flow capacity. It is
not necessary to open this valve to the full open
position to provide full flow to the process. Opening
this valve fully poses two serious problems. The
first problem is safetyrelated. In many applica
tions, cylinders with these valves are used in tight
quarters (e.g., gas cabinets) or behind barricades.
These space constraints often prohibit the stem
from being fully rotated when the valve is operat
ing. This valve requires approximately three full
turns from full open to full close. In the case of
Note: Teflon is a registered trademark of E.I. du Pont de Nemours and Company. Figure 3
Handwheel-Operated Packed Valve
an emergency, it can take 15 to 30 seconds to
close the valve, depending on space and operator
stress. However, if the valve is opened to the rec
ommended ¼ to ½ turn, the valve can be quickly
closed with minimal operator exposure. The second
benefit of only opening the valve the recommended
¼ to ½ turn is the protection of the upper section
of threads.
The threads are in the wetted gas stream and, due
to the corrosive nature of many of the products
where these valves are used, the threads can
become jammed with corrosion byproducts. If
the valve is opened to the recommended ¼ to ½
turn and the threads become jammed, the upper
threads usually remain clear. This allows the
operator to further open the valve and to free the
threads. The proper operation of this valve requires
the use of the proper wrench. Air Products recom
mends using the square stem valve wrench, com
modity code E99P38WRENCH, to operate these
valves (except on highly reactive gases such as
fluorine, ClF
3
, etc.). This wrench has a square hole
sized to fit the stem and an openend wrench on
the opposite end that fits the packing nut. The
Air Products recommended opening procedure
for this valve is as follows:
1. Connect the cylinder to the system.
2. Snug the packing nut with the wrench
(35 ftlbs).
3. Place the wrench on the stem and slap the valve
open by striking the wrench with the palm of
the hand.
4. Continue opening the valve until it is ¼ to ½
turn open.
Where possible, leave the wrench on the valve so
that a quick closing of the valve can be done in the
event of an emergency.
Recommended Closing Procedure: Using an
appropriate wrench, tighten the stem by pulling the
wrench to the closed position. When the valve is
closed as tightly as the wrench can be pulled, give
the wrench a closing slap with the gloved palm
of the hand. The minimum closing torque for this
valve is 35 ftlbs, but it is not uncommon for some
valves to require as much as 60 to 80 ftlbs to fully
seal.
Caution: Some valves may become worn or col
lect debris in the seat, causing difficulty obtaining
a complete seal. In these ca