Part 21 Report - 1996-732
ACCESSION #: 9612160224
Valve Company o Williamsport, PA 17701
W. G. KNECHT
November 27, 1996
Mr. Jerry Carter
Events Assessment Branch
Washington DC 20555
Subject: A/DV 1878 Class Piston Check Valves
Dear Mr. Carter:
Per our discussion this date the enclosure is the latest copy of our
report to FP&L regarding the piston check valve problem.
Should you have any questions please do not hesitate to call Floyd
Bensinger, our Engineering Manager, or the writer.
ANCHOR/DARLING VALVE COMPANY
William G. Knecht
cc: F. A. Bensinger
Anchor/Darling Page 1 of 4
701 FIRST STREET
P.O. BOX 3428
WILLIAMSPORT, PA 17701-0428
FAX: (717) 327-4805
Florida Power and Light Company
St. Lucie Plant
P.O. Box 128
Fort Pierce, FL 24954
November 20, 1996
Attention: D.J. Denver
St. Lucie Engineering Manager
Subject: A/DV 2"-1878# Piston Check Valves
Reference: 1. FP&L JPN-SPSL-96-0372, August 16, 1996 Letter
2. A/DV S.O.'s ET401 and RZ814
3. A/DV Test Report No.'s RZ814, Test Report of Flow
Test on a 2"-1878# Globe Piston Check Valve,
October 2, 1996
A/DV apologizes for the delay in responding to the referenced FP&L
letter. We had hoped to receive application responses to our
notification letters but as of this writing we have not received any
A/DV has performed a design review of the piston check valve with
the intent to address the functional and re-assembly problems experienced
at St. Lucie. The following areas were addressed as noted:
A. Pressure Seal / Bonnet Area Items
1. Bonnet Retainer Capscrews
FP&L reported having difficulty in sealing the ADVanseal using
the capscrew without pressure. The current capscrew is a 5/16"
diameter capscrew. A 1/2" diameter capscrew will be used in
the future. This will provide approximately three (3) times
the gasket load.
2. Galling of the Bonnet Retainer Threads
FP&L has experienced galling of the bonnet retainer threads.
The current retainer is made of 316 stainless steel with chrome
plated 12 series threads. A/DV is evaluating replacing this
design with a 17-4PH bonnet retainer (no chrome plating) with 8
series threads. Assuming successful completion of the new
bonnet retainer evaluation, this design will be put in place.
A/DV plans to include the philosophy of both enhancement with the
smaller piston check valves. These two (2) enhancements will affect
inventory and part interchangeability.
B. Cleaning / Drying of Valves Prior to Shipment
A/DV has evaluated several methods to assure complete drying of the
piston check valves prior to shipment, i.e. disassembly, baking,
etc. We have concluded that the most effective method is to
disassemble the valves after hydrostatic testing, dry the parts and
reassemble without the gasket and anti-rotation pin (Part No. 258)
installed. The gasket and anti-rotation pin will be packaged with
the valve and a tag placed on the valve requiring installation of
these two (2) parts after valve installation.
C. Valve Performance / Functional Items
1. Disc Guide Area of Body Neck Bore
We evaluated this area to determine if the body guides could be
improved. Several methods were evaluated, i.e., sleeving the
body bore with hardened material, reshaping the exhaust port,
etc. All methods are costly. The conclusion was reached that
the above changes were cost prohibitive and the better
resolution is to use a smaller valve for oscillating flow
application in order to place the disc in a more open position
where it is better guided by the body.
C. Valve Performance / Functional items (Continued)
2. Disc - Body Material Couple
It was stated by FP&L that fretting is more apt to occur where
a large difference in material hardness exists. A/DV selected
the body-disc material couple for wear resistance, galling
resistance and castability, weldability of the bodies.
A more important factor to reduce the potential for fretting is
reduced stress levels. A/DV does not plan to change the body
or disc materials. As discussed in A.1. above and in the later
root cause analysis, use of a smaller valve would resolve this
3. Rough Machining left in the Body Neck Bore
In May, 1993, A/DV had changed its rough machining process to
setup and rough cut the neck bore and seat pocket using the
same setup method and single point tooling-boring as the finish
machining process. Prior to this time the neck bore was rough
machined on a radial drill. This drilling process was not
always performed on the same centerline as the final machining
and the drill had a tendency to tail off center. This area has
been resolved as described above in May, 1993.
4. Ratio Guide Length - Disc Diameter
A/DV's design criteria limits the potential disc tilt to less
than 1/2 degree, and requires a ratio of one (1) or greater for
the disc, guide length to diameter. The 2"-1878# Piston Check
disc has a ratio of 1.12:1. Both A/DV's design criteria and
the 2"-1878# design are representative of A/DV and competitive
valve designs which have been proven to be successful in most
A/DV evaluated the as found condition of the piston check valve that
stuck open. To assist in our root cause analysis, we performed flow
tests on two (2) 2"-1878# Piston Check valves (one (1) valve
returned from FP&L, S/N ET401-9-6). Reference No. 3 Report,
enclosed, documents the task and results. The testing was performed
to evaluate valve performance at various forward flow rates. The
test conclusion was the valve always closed when forward flow ended.
Root Cause (Continued)
As a result of our evaluation of the FP&L failed valve and our
testing, we have concluded that the root cause is the disc
oscillation, caused by the reciprocating pump, causing fretting to
take place in the valve body disc guide area. The fretting area
provides a configuration in the body guide that allows the disc to
stick open without forward flow and with reverse flow.
A/DV's recommendations to eliminate the valve operational problem
are (preferred listed first):
A. Use of in-line check valves in reciprocating pump applications.
This valve design provides better wear resistant materials as
disc guides throughout the entire valve stroke.
B. Use of smaller piston check valve (valve size or reduced port)
in reciprocating pump applications to more fully open the disc
where better body-disc guiding is available. Attached are
graphs of flow rate versus disc position and Cv versus disc
position to be used to evaluate T-pattern piston check valve
size selection. Where a smaller T-pattern piston check valve
produces too high a pressure drop, use of a Y-pattern piston
check valve may resolve this concern.
T-pattern and Y-pattern piston check valves and in-line check valves
are within A/DV's product lines. Availability of Y-pattern piston
check valves is scheduled for the second quarter of 1997.
If further discussion is required on the above, please feel free to
ANCHOR/DARLING VALVE COMPANY
Floyd A. Bensinger, P.E.
Manager - Engineering
bcc: J. Chappell G. Parks
T. Johnson J. Tarbutton
W. Knecht H. Wescott
G. Kneiser F. Velez
Chart "2" Smaller T-Piston Check Valves" 3 pages, omitted.
Figure "2"-1878 FULL PORT SOCKET ENDS STAINLESS STEEL PISTON CHECK VALVE
NON-COBALT TRIM" omitted.
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