1. Keywords: Check valve • Nozzle check • Slam • Water hammer W AT E R & W A S T E WAT E R
Water hammer in process piping:
How to avoid this by selecting the
right check valve
As pipelines grow longer
the swing check valves’
travel distance to closure in
high volume of process flow
becomes greater causing
water hammer or “slam”.
The industry currently utilises
several types of check valves
and these tend to slam upon
closure in reverse direction – a
common problem. Reviewing
the process piping to find a
more suitable check valve
becomes necessary. Mr. Gobind
Khiani, an AIMS Manager at
Cenovus Energy Inc., shares Swing Check vs Dual Plate Spring loaded design.
his know-how regarding water
hammer in process piping and 3. The swing check valve is not closing Prototypes were developed and tested at
the role of nozzle check valves fast enough allowing water hammer Delft Hydraulic Laboratories during the
in its prevention. to slam the disc into the seat. 1960’s and have been in operation for over
Continued slamming has damaged 50 years with no sign of failures in various
the sealing surface preventing the industries and applications.Compact design
valve from sealing fully. tested at the Utah State University and has
By GobindKhiani, Cenovus Energy Inc.
been in operation since 1975 in various
The signs of excessive “swing check
industries with no failures reported.
slamming” include grout cracking beneath
C
heck valves are emergency Factors to consider in nozzle check
pump and motor pads and base, damage
backflow preventers typically applications include during normal or
to electrical cable to the motor, and
used around critical equipment. minimum operation where fluid flow is
increased vibrations caused by induced
These rely on backflow to operate shut less than 10 ft/sec, air flow is less than
pump and motor misalignment. Pressure
and flow to open and how much it is 400 ft/sec and saturated steam flow is less
gauges and switches become abnormally
open is dependent on the flow condition. than 200 ft/sec. Another factor is when
out of calibration as well as cracked valve
Among the various types of check check valve locations are downstream
seat surface, excessive piping header
valves are swing check valves. However, of pump elbows or other turbulence
displacement and heat exchanger
problems arise with this type of valve, source and when said valves are located
tube failures caused by pump cycling
such as leakage through its seat due to the downstream of the pump or compressor.
activations.
following reasons: In addition, nozzle check valves should
1. The valve is installed in its application Nozzle check valves be in a system where pressure surges
in which it is not suitable. Most swing Nozzle check valves are check valves that during flow transients and valve closure
check valves cannot be installed prevent reverse flow. These have an axial produce pressure spikes approaching the
vertical with the flow passing from disc movement with short stroke and system design pressure. Essentially, when
through above. a venturi nozzle-style, which maximises previously installed check valves have
2. The swing check valve was installed flow impact on disc and minimizes internals that are worn or damaged at the
less than 10-pipe diameter away from pressure loss. The valves have better hinges, bushings or seating surface, nozzle
upstream pipe fitting or pump.This dynamic response, high reliability and check valves are the best alternative; also
results in turbulent flow, disc chatter and most significantly, non-slam operational in positions where check valves are known
ultimately damage to the sealing surface. characteristics. for sticking.
www.valve-world.net November 2012 1
2. W AT E R & W A S T E WAT E R
About the author
GobindKhiani, B.Sc.,
MEng graduated
with a B.Sc. from
the University of
Poona in India
and a Masters in
Engineering from
the Universityof
Calgary in Canada. His career began
with the Transmark Group in UK and
Dubai. After 16 years, he moved to
Canada and worked at VELAN Valves,
Crane Energy and currently works
A cross section of Nozzle Check Valve design. at Cenovus Energy Inc. as an AIMS
Manager.
Why and when? and reciprocating compressors Gobind has worked in the oil & gas
Nozzle check valves are clean service (pulsating flow). and nuclear industries since 1992 and
valves with high reliability, low maintenance Nozzle check valves are ideal to use has been involved with valves since
and relatively low pressure losses.These with liquids e.g. oil; water (sea, potable); day one. He has helped numerous
application-sensitive valves have the ammonia; hydrocarbon liquids etc.; rapid users in selecting the right valve
technology known to eliminate water deceleration systems, e.g. multi-pump product for the desired
hammer and potentially destructive surge installations, upstream of vertical column, process conditions and helped
pressures. The latter is usually associated upstream of air vessel or surge tank; gases improve asset integrity management
with conventional check valves used with e.g. hydrocarbon, refrigerants, nitrogen, programs.
centrifugal compressors when surging hydrogen etc.
2 November 2012 www.valve-world.net
