has spent 41 years in the valve industry, including his current
nine-year stint as a technical sales specialist with Assured
Automation. During his career, Mr. Siedler has worked with bar stock
globe control valves (with customized trim), rising-stem three-piece,
three-way globe valves and spring and diaphragm-actuated diaphragm
control valves. He has experience with sizing valves for chemical and
pharmaceutical applications and has provided technical input for valve
applications in the nuclear and fossil power industries. Mr. Siedler
has also worked with the NAVSEA (www.navsea.navy.mil
) engineering group in Crystal City, Va. on valve applications for the military market. Mr. Siedler can be reached at firstname.lastname@example.org
For many applications, valve sizing and selection will determine the
ultimate success or failure of the larger process. In your opinion,
what are some key steps end-users can take to ensure the proper sizing
and selection of valves?
For the purpose of the following line of questions, let’s define the
type of valves we are discussing. Years ago, control valves were
generally thought of as throttling control valves. Today, however, many
consider actuated on-off valves as control valves as well. For the sake
of this discussion, I am going to assume we are considering both.
Throttling control valves include the rising-stem type of valves, both
soft-seated and metal-seated, and quarter-turn valves, both soft-seated
and metal-seated with standard trim or characterized trim, coaxial,
angle-seated, and diaphragm valves.
the appropriate type, or types, of valves for the application have been
identified, the user should then attempt to determine the “approximate”
size of the valve that is required. A user can effectively determine a
rough valve size either by using an appropriate formula or sizing
valve selection, users should first analyze the material of
construction of the valve based upon compatibility with the media being
handled. If there are a number of choices, select a few and rate them
regarding their relative compatibility. The end-user is generally the
best source for this determination, because in the majority of cases,
it is the user that has prior experience with the media being handled,
and they know more about it than anyone else. For example, the users
may know the piping material that has been successful in handling their
particular media. Quite often, the media is a unique mixture of
chemicals. Standard chemical compatibility charts may be inappropriate
for materials of construction in such cases.
the characteristics of the media you are handling – is it a relatively
easy product to handle (air, water, inert gas) or is it toxic,
corrosive, abrasive, carcinogenic; does it polymerize, solidify,
crystallize; does it contain fine particulates; is it a slurry, does it
have a high coefficient of expansion? All of these characteristics
should be considered.
the size, the materials of construction, the characteristics and the
pressure/temperature of the media, as well as the pressure class of the
piping system, the end-user can now look for the appropriate type (or
types) of valve to handle the application. Armed with this information,
the user can approach valve vendors for guidance in choosing the
appropriate valves for the application. And once the appropriate valve
has been chosen, the user can proceed to the task of sizing.
sizing is the procedure of determining the appropriate flow coefficient
(Cv) for the valve and the application. End-users may want to calculate
the Cv required or use a particular manufacturer’s sizing program (if
one is available). When sizing a valve, it is very important to use
accurate information and not to make assumptions.
manufacturers tailor their sizing programs to the type of valves they
offer. Most sizing programs utilize a simplified sizing technique.
These programs have certain parameter limitations. Applications that
are beyond the limitations of such programs must rely on more intricate
mathematical sizing calculations. Sizing programs will likely present
different limitations depending on whether the media is liquid or
gas/steam.* (Please see the application data provided below for
accurate valve sizing.)
the case of throttling control valves, the customer must determine how
accurately the selected valve will have to produce the determined CV.
This is one of the areas where valve sizing and valve selection are
other factors may affect the accuracy of the valve assembly, throttling
valve types generally fall in the order provided below from
most-accurate to least-accurate:
1. Rising-stem valves (i.e., globe valves) with custom-machined all metal trim (plug and seat).
Rising-stem valves (i.e., globe valves) with custom-machined soft trim
(metal plug and soft seat, metal seat with soft insert).
3. Rising-stem valves (i.e., globe valves) with standard all-metal trim (plug and seat).
4. Rising-stem valves (i.e., globe valves) with soft trim (metal plug and soft seat, metal seat with soft insert).
5. Quarter-turn valves with metal seats and characterized trim.
6. Quarter-turn valves with soft seats and characterized trim.
7. Quarter-turn valves with metal seats and standard trim.
8. Quarter-turn valves with soft seats and standard trim.
After selection and sizing, the valve assembly can be configured.
Configuration includes selection of the appropriate actuator (pneumatic
or electric) and/or positioner (if required and for throttling
applications). The user must determine if the actuator is to be
fail-open, closed, or double-acting. If there is a positioner, what is
the control signal and are other accessories required (i.e. limit
switches, solenoid valves, etc)? What size actuator is required to
properly actuate the valve? If pneumatic, what is the air-supply
pressure? If the actuator is electric, what is the voltage available?
For electrical components, what is the NEMA rating required? These are
some of the questions that generally should be addressed during the
In your experience, what are some of the common errors end-users make
in the area of valve sizing and selection? In those applications where
improperly sized valves result in performance problems, what are some
of the common reasons the valve was improperly sized in the first place?
In many cases, users today are not familiar with the wide variety of
valves available, and, as a result, inappropriate valves are commonly
specified. Often, to be “safe,” a valve larger than required is chosen.
This factor, along with the popularity of ball valves, has resulted in
the over-specification of full-port ball valves. Ball valves are
wonderful devices; they are extremely versatile and quite often very
cost effective, but they are not a panacea. If a standard-port valve or
a valve with a reduced Cv is acceptable, there are very cost-effective,
compact, fast-acting, pneumatically operated and electrically operated
valves available – some of which are available for only clean services,
while others support more general services. There are also other small,
fast-acting valves that can handle very high cycle rates and even
support steam applications better than ball valves. If the application
is corrosive, toxic, abrasive, or slurry and it polymerizes,
crystallizes, and/or solidifies, a ball valve may not be the best
prevalent problem is that users often “assume” various data points in
their calculations or sizing program inputs, thus producing erroneous
Prior to engaging in the valve sizing and selection process, what
application data should an end-user be sure to gather to ensure success
and streamline the sizing and selection process?
The following information is generally required:
I. Incompressible Flow
a. Data required for liquids:
- Inlet Pressure
- Pressure Drop
- Specific Gravity (In the event of an application with mixed chemicals, this
is a value that depends significantly on the knowledge of the end-user)
- Vapor Pressure
- Recovery Factor
II. Compressible Flow
a. Data required for gases or vapors:
- Inlet pressure
- Pressure drop
- Specific Gravity
b. Data required for steam:
- Inlet pressure
- Pressure drop
- Saturated temperature
While valve manufacturers offer a variety of tools to assist users with
valve sizing and selection, it can be a little unnerving for end-users
to rely on a piece of software for the specification of technology. In
your opinion, how effective are today’s valve sizing and selection
tools in identifying the appropriate solution for a given application?
latest generation of online valve configuration tools provide a
simplified approach for end-users to perform such tasks as actuator
selection and evaluating and selecting various valve accessories.
I believe that, for the most part, sizing programs are an improvement
over mathematical calculations and slide rules. They reduce the
instances of errors, but they are, as anything else, only as good as
the data provided and used within the intended parameters of a
simplified sizing technique typically suitable for an electronic sizing
program. Some valve applications are simple, others are complex. These
two extremes of sizing difficulty – and the fact that one is suitable
for electronic sizing and the other is not – can add confusion and
mystique to this task.
example of a simple application would be potable water flowing at 150
F. A difficult application would be a corrosive, toxic, mixed chemical
media with entrained solids flowing at high pressure and temperature.
The valve selection process for the latter application would be far
more complicated that the selection process for the former application.
the best of my knowledge, there are no formalized valve “selection”
tools. I believe this is primarily because of the complexity of the
valve selection process for a significant number of applications, as
well as the number of possible valve solutions available for a broad
range of application scenarios.
That said, there is, however, a relatively
new class of tools for valve users and specifiers called valve
configurators. Configurators are generally online tools that aim to
simplify actuator selection and the addition of various accessories to
allow the user to build a virtual valve assembly, create the assembly
part number, and either order the assembly online or use the
accumulated information for specification and/or requisition purposes.
Some end-users I’ve spoken to in recent years have expressed
frustration at the complexity and cumbersome nature of valve sizing and
selection. How has the latest generation of specification tools evolved
to provide a more intuitive and streamlined approach on valve sizing
I can understand the frustration of some end-users. But as I mentioned
before, some applications are fairly simple, while others can be
extremely complex. This is the reason I went into so much detail above.
I was trying to convey the possible complexities of some applications.
You have the valve selection exercise, the valve sizing exercise, and
the valve assembly configuration exercise, all of which are
feel the valve assembly configurator offers a more intuitive and
streamlined approach for end-users, but it is neither a valve selection
nor sizing tool. This tool would be better described as a valve
actuator sizing tool.
I believe online valve configurators are the most exciting recent
advance in modern valve application tools. These tools can save the
user a significant amount of time by enabling quick-and-easy
configuration, identification and pricing of valve assemblies. Further,
configurators can be used, in many instances, to explore and compare
various options in a minimum amount of time.
When looking back and into the future, what are some of the key
improvements you’ve seen in the way valves are sized and selected today
as compared to the past, and how do you see the sizing and selection
process evolving to provide added improvement going forward? How is
valve sizing and selection today better than it was yesterday, and how
will it be better tomorrow than it is today?
The only real improvement I‘ve seen in this arena is the implementation
of the online valve configuration tool. I believe there is significant
potential for improvement in this technology by increasing the breadth
of the types of valves included.
valve sizing programs were the last significant improvement in sizing,
and they have been around for quite a while. I really don’t see any
improvement coming except for the continued proliferation of
essentially the same programs.
frankly, I believe valve selection is worse today than it was
yesterday. I believe that, due to the complexity of valve technologies
and applications today, selection must be performed by a knowledgeable,
experienced and objective specialist who is familiar with the various
types of valves on the market and the media that is being handled. Such
individuals can be assets to the sizing and selection process because
they bring with them a solid understanding of present-day material
compatibility issues. However, due to the downsizing and/or demise of
our pharmaceutical, chemical and architect engineering firms, many
mechanical engineers with valve expertise have been lost.
such, I don’t see an improvement in valve selection unless or until
corporations recognize the importance of valve expertise within their
organizations and do something about it. Even then, I believe it will take years to develop the experience and knowledge needed.