dashpot development test for fftf cold leg check valve

D A S H P O T D E V E L O P M E N T T E S T F O R F F T F C O L D L E G C H E C K V A L V E

D. K. SHARMA, R. HENSCHEL & M. KRAWCHUK

Foster Wheeler Energy Corporation, John Blizard Research Center, Liringston, New Jersey 07039, USA

(Received: 28 November, 1976)

ABSTRACT

This paper presents work that was performed to develop the dashpot for the Fast Flux Test Facility Cold Leg Check Valve. The portion covered herein involved the water testing Of two basic dashpot designs and their modifications. The two basic designs included an annular and a non-annular concept. The programme consisted oJ subjecting each dashpot to a series of tests in water to investigate its filling, recocking and damping behaviour. The test results discussed herein showed the non- annular design to be superior and to meet perJormance requirements in virtually all cases.

INTRODUCTION

The Fast Flux Test Facility (FFTF) reactor coolant system consists of three cooling circuits, of equal capacity, in parallel. Each circuit is comprised of a radioactive primary heat transport loop and a non-radioactive secondary heat transport loop. Thethree primary loops have a common flow path through the reactor vessel but are otherwise independent in operation. Figure 1 illustrates the process flow concept for one of these identical primary loops.

Check valves were included in the Cold Legs of the primary loops to prevent reverse flow in the loops in the event of a pump failure. This permits the maximum possible flow through the reactor core to be maintained. A dashpot was recommended for inclusion in each check valve to limit the surge pressure (fluid hammer) resulting from the rapid closure of the valve disk due to the reverse flow (Fig. 2). This recommendation was made after recognising the numerous practical problems that exist with other surge pressure reducing methods, some of which are discussed in previous publications.I-3

23 Int. J. Pres. Ves. & Piping (6) (1978)--:~ Applied Science Publishers Ltd, England, 1978 Printed in Great Britain

24 D. K, SHARMA, R. HENSCHEL, M. KRAWCHUK

Pump Motor..

Reactor Containment Floor ' ~ ~ Cover . ~ '-~'--"' J

~ L i n e M Gas Line ~ _ ~ To Reactor S o d i u m _ _ , . . ~ . ~ ~ - - l ~ ? ~ -,: - T r , Inlet ~ ~ r ~ " I ~ ~1 l-~ ~ F low / Cold Leg Cold Leg;

I I I I 1 - ~ I IIII Meter Check Isolation~ vo,vo Valve

Pump I Reactor ~,

Fig. 1. Primary heat transport system hydraulic profile (information only).

914

406

OUTLET

INSPECTION PORT

\ \

' DISK- CLOSED POSITION 'i

DISK-OPEN POSITI'ON ..... I,

'! 1727

9ASHPOT

406 -~'-I

Fig. 2. FFTF primary system Cold Leg Check Valve. Dimensions in mm.

DASHPOT DEVELOPMENT TEST FOR FFTF COLD LEG CHECK VALVE 25

There is little or practically no published information available to develop a dashpot design for elevated temperature liquid sodium service. Therefore, an experimental programme was undertaken to develop such a design utilising full size test units. The experimental programme consisted of:

(1) Developmental water tests at the Foster Wheeler Energy Corporation (FWEC) to obtain a preliminary dashpot design. Water was chosen as the initial test medium for reasons of safety, economy and expediency.

(2) Final water tests of the preliminary design, at Colorado State University (CSU), to develop a prototypical design.

(3) Acceptance tests in air and freon and tests in liquid sodium of the prototypical design, at FWEC.

In this paper, the details of the development water tests performed at FWEC are primarily discussed. This discussion includes the description of the test rig and test procedure, followed by the evaluation of the test results. The paper also contains a brief description of the final water tests at CSU and concluding remarks.

DESCRIPTION OF DASHPOT CONFIGURATIONS

Two basic dashpot designs, shown schematically in Fig. 3, were tested to evaluate their filling, recocking and damping characteristics. The first was an annular design in which fluid flow occurred through the clearance between the piston and cylinder.

Dashpot ~ " ~ Cylinder-~.

(a)

Doshpot Piston

I

I I

\ Fluid flow through onnuJar cJeoronce

, , j O r i f i c e

P,s,oo .,no

,11 = \ Doshpot Doshpot Piston Flow through orifices

Cylinder in cylinder wall

(b)

Fig. 3. Schematic drawings of (a) annular and (b) non-annular dashpot designs.

26 D.K. SHARMA, R. HENSCHEL, M. KRAWCHUK

Port for inserting Pressure Transducer

Dashpot Cylinder

17e -"1~1

! 1 3 3

Fig. 4.

/ /

t

f/Labyrm~h Groove

o~ 0 3 0 ~ 076

Dashpot Piston

J i

Dashpot configuration No. 1. Approximate dimensions in mm.

This annular design included dashpot configurations No. 1, 1A and 1B. The second was a non-annular design which contained orifices in the dashpot cylinder wall and piston for fluid flow. This design included dashpot configurations 1C, 1D and 2.

Dashpot configuration No. 1 is shown in Fig. 4. The inside diameter (i.d.) of the dashpot cylinder was approximately 95 mm while its outside diameter (o.d.) was about 146mm. The annular clearance between the piston and cylinder was approximately 0-0635 mm. The piston had a total length of about 202 mm. There were 45 'V' type labyrinth grooves which were machined radially into the outside surface of the piston. A spring was installed between the bottom of the cylinder bore and the piston to recock the piston.

Configuration No. 1 was modified to configuration No. 1A by changing the shape and size of the grooves in the dashpot piston. As shown in Fig. 5, the width and depth of these grooves were greater than the grooves present in configuration No. 1.

Configuration No. 1B was obtained after modifying the piston of configuration No. IA. The piston of configuration No. 1B contained square wave grooves, as shown in Fig. 5. Figure 6 shows a photograph of the various components of configuration No. lB.

Configurations No. 1C and 1D were simulations of a non-annular design. They were modifications of configuration No. 1B. Their basic configuration is shown in Fig. 7. Each contained a rubber 'O' ring around its piston and had an adaptor inserted in the pressure port of its cylinder. At any one time the adaptor contained one of two different sets of orifices. The set for configuration 1C consisted of 27


2 Ref

Detail Piston Groove d a t u ~ . ~ . ( ~ '03

Fig. 5.

0 76

Detail Square Groove datum / 0 69 typ

~ Edges must be free of burrs and

~ 0.69

Piston groove detail for dashpot configuration Nos. 1A (top) and 1B. Approximate dimensions in mm.

Retainer Prate

Cyl inder Piston Spr ing

Fig. 6. Photograph showing configuration No. lB.

28 D. K. SHARMA, R. HENSCHEL, M. KRAWCHUK

1 ~ . . . . / O r i f i c e Stack Adaptor

S Doshpot Piston

Fig. 7. Sketch of dashpot configuration No. IC and ID.

orifices stacked over each other 'in-line'. The set for configuration 1D consisted of 27 flip-flop orifices stacked over each other. All orifices contained a 3-18-mm diameter hole for fluid flow and a 3.18-mm diameter hole for an alignment rod to stack them properly.

Configuration No. 2 was a non-annular design, as seen from Fig. 8. It was not a modification of any of the previous dashpot units. The cylinder of configuration No. 2 contained two radial orifices which had diameters of 1.38 mm and 3. ! 8 m m A port near the bottom of the cylinder was also made to include a pressure transducer. The piston of configuration No. 2 was approximately 260 mm long. Its o.d. was

Pressure Spring Cylinder ~Cover Plate Transducer Port-._____ '\\ " ~ j Stellite Sleeve

~ ~ ~ 7 - ~ A ~/Plslon !

. . . . . . .

I ! . . . . . . . 260 _ ~._]

Fig. 8. Sketch of dashpot configuration No. 2. Approximate dimensions in ram.


about 95 mm. It contained an inconel piston ring to seal most of the annular clearance between the piston and cylinder wall. A stiffer spring was installed in this design than that used in the annular designs.

With the exception of the springs and/or the piston rings, all dashpot components were fabricated from 304 or 316 stainless steel. The springs and piston rings were made of either 300 series stainless steel or inconel.

DESCRIPTION OF TEST RIG

The rig used for the developmental water tests is shown in Figs. 9 and 10. The rig consisted of a vessel to contain water, a high-pressure pumping system, and its supporting structures, which had provisions for mounting the dashpot. The components of this rig were made of carbon steel.

Simulation of the dashpot actuation by the check valve disk was achieved by the hydraulic cylinder and associated control system. A Linear Variable Differential Transformer (LVDT) gauge was used to measure the displacement of the dashpot piston. A pressure transducer was inserted through the pressure port in the dashpot cylinder to measure the internal pressure in the cylinder.

Two chromel-alumel thermocouples were utilised to measure temperature. One thermocouple was located on the body of the dashpot to measure its temperature and the other was installed in the vessel to measure the water temperature. A variac controlled, resistance heater was used to heat the water in the vessel whenever testing was done at elevated temperature.

Vessel

L _

Cover Plate

J Bellows / LVDT

] 4

Actualor

!~Cover Plate

3 Hydraulic Cylinder

m

Dashpot Assembly

Fig. 9. D a s h p o t deve lopmen ta l water test rig.


Fig. I0. Photograph showing water test rig prior to mounting of dashpot.

TEST PROCEDURE

The developmental water test began with filling, recocking and damping tests of configuration No. 1 in water at approximately 77°C. Water at this temperature closely simulates the sodium density at the FFTF operating temperature of 427 °C. However, testing of configuration No. 1B in 77°C and 21°C water led to the conclusion that the future testing could be done in 21 °C water (see Table 1). With the exception of heating the water for testing at 77 °C, the general procedure for various developmental tests was the same and is given below.

A given test began by filling the vessel containing the dashpot with water. The dashpot was then allowed to fill for approximately 15 min. To check the filling ability of the unit, its piston was stroked manually. Upon doing so, if the dashpot was only partially filled, air bubbles were seen through the top hole in the vessel. To guarantee that the dashpot was completely filled prior to the recock and damping


tests, the piston was stroked manually a number of additional times until no air bubbles were seen.

The tests for evaluating the dashpot recocking and damping behaviour began by applying a relatively small force to the dashpot piston, pushing it forward. The force was generated by a supplementary pumping system. The resulting pressure in the dashpot cylinder, piston displacement and temperatures of the water and dashpot body were then recorded. The hydraulic piston of the pumping system was then retracted and the dashpot was examined to determine if it had recocked and, if so, how long it took to recock. The recock time was determined using a stopwatch manually. Following this, the hydraulic force of the pumping system was raised and the test procedure just described was, in general, repeated until a desired maximum pressure in the dashpot cylinder was reached. In the testing of dashpot configurations No. 1A and 1B, the desired maximum pressure was kept at approximately 12,]300 kPa. As stated later the dashpot damping behaviour was not sensitive to the change in the dashpot cylinder pressure beyond 6900 kPa; hence, the desired maximum pressure for subsequent tests was established at approximately the 6900 kPa level.

DISCUSSION OF DEVELOPMENTAL TEST RESULTS

The test results from each dashpot development test were compared with the following requirements:

(1) Dashpot must fill completely. (2) Dashpot must recock within 30 sec. (3) Dashpot damping factors (DDF) should be in the range of 200 + 10 when

the pressure in the dashpot cylinder is in the range of 4900 + 30 kPa. This optimal range of DDF values was established by performing a fluid dynamic transient analysis of F F T F primary loop check valves. 4 As shown in the Appendix, the DDF values characterise the hydraulic resistance imparted by the dashpot piston, which will control the closure rate of the valve disk in actual plant life. The valve disk closure rate then influences the surge pressure (fluid hammer) in the primary loop.

The test results for all dashpot configurations are summarised in Table 1. The D D F values, as a function of pressure in the dashpot cylinder, are presented in Figs. 11-13.

As seen from Table 1 and Fig. 11, configuration No. 1 did not meet the requirements stated above. That is, it did not fill completely and its recock time ranged from 30 to 55 sec which was more than the maximum allowable time of 30 sec. Furthermore, its DDF values were in the range of 29 to 33, as compared to the desired range of 200 _+ 10 for the dashpot cylinder pressure range of 4900


TABLE 1 S U M M A R Y O F D A S H P O T D E V E L O P M E N T T E S T IN W A T E R

Dashpot Water Did dashpot sati.~v development General comments configuration temperature test requirements?

° C . . . . . . . . . . . .

Filling Recacking DDF requirement requirement requirement

1 77 No No No (1) Recock time ranged from IA 77 No No No 30-55 sec against

maximum acceptable of 30 sec

I B 77 No " No (2) DDF values ranged from 21 ° " " 20 to 40 against desired

range of 200 4-_ 10 1C 21 " " Yes 1D 21 ~ " No 2 21 Yes Yes No

Maximum DDF was 40 (1) recock time 4-6 sec (2) DDF values close to the

desired range

"No test was conducted to determine these characteristics of the dashpot.

22O

2OO

180

D 160

D 140

F 120

; 0 0

8O

6O

, Desired DDF Region

( estoblished analy t ica l ly )

o C o n f i g u r a t i o n I

z~ Configuration I A

t:] Configuration I B

( Water - 21"C )

4 0

2 0

0

v Configurat ion IB

~z~ ( W a t e r - 7 7 ° C )

_ ~ ~ ~ ~, o %

o

_ °° ~°od~ ~ o

I [ I I I I I I I I 2 5 4 5 6 7 8 9

Dashpot Cylinder Pressure - kPa

oo

I I I I0 I I 12x lO 5

Fig. 11. Plot of DDF versus cylinder pressure-annular dashpot configurations.


3 0 0 0 F

2500 1-

2O0

180

D 160

D 140

F 120

I00

80

6O

4O

2O

0

Fig. 12.

Desired DDF Region (establ ished analytically) ~'~

• 0 O• 0 •

0

o ¸

z~

Both radial orifices ( 1.38, 3.18mm ) open

318rnm orifice closed (piston passed it)

318mrn orifice closed (using blank plug )

Both orifices closed ( piston passed them )

o •

I I I L I I l I 2 3 4 5 6 7xlO 3

Dashpot Cylinder Pressure - kPa

Plot o f D D F v e r s u s c y l i n d e r p r e s s u r e d a s h p o t c o n f i g u r a t i o n N o . 2.

_+ 30kPa. The damping provided by this dashpot decreased with increasing pressure in the dashpot cylinder when the dashpot cylinder pressure was below 6900 kPa. However, the damping behaviour was not sensitive to the change in the dashpot cylinder pressure beyond 6900 k Pa.

In view of its poor performance, configuration No. 1 was modified. The modified dashpot (configuration No. 1A) had a recock time in the range of 30 to 40 sec, as compared to the recock time of 30 to 55 sec for configuration No. 1. Furthermore, configuration No. IA had DDF values that were higher than those of configuration No. 1. These improvements were probably the result of the new piston land configuration. In spite of these improvements, configuration No. 1A did not meet any of the stated requirements.

As with configurations No. 1 and 1A, configuration No. IB did not satisfy the stated requirements. The damping provided by this unit was less than that of configuration No. 1 and IA. Configuration No. 1B was, however, used for another purpose also. As seen from Fig. 11, its damping performance was in the same general range when tested in water at approximately 21 °C and 77°C. This led to


2 2 0 -

2 0 0 - @ o 0

1 8 0 -

1 6 0 -

140 -

120 -

I 0 0 -

8 0 -

6 0 - o

40

2O

0 L 0 l

8 FL, ~ Desi red DDF Region o ~ ~ L~ ( e s t o b l i s h e d gno ly t i ca l l y )

0 0 0

z~: C o n f i g u r a t i o n IC

o Configuretion IC (orifices retighlened )

O: Configuration ID

1 I I I ] L I I I I I 2 5 4 5 6 7 8 9 I0 II 12xlO 3

D a s h p o t C y l i n d e r P r e s s u r e - k P a

Fig. 13. Plot of DDF versus cylinder pressure-dashpot configurations No. IC and 1 D.

subsequent testing of all dashpots in water at 21 °C (see Table 1). The next test was performed on a non-annular design (configuration No. 2). The filling and recocking characteristics of configuration No. 2 were satisfactory with one or more of its radial orifices open. Most of the filling was observed to take place during the first several minutes of testing. This unit had a recock time of 5 to 6 sec which was well below the maximum acceptable recock time of 30 sec.

The damping of configuration No, 2, with both radial orifices open, was significantly low. During the initial part of the piston stroke, D D F values were in the range of 8 to 9 in the dashpot pressure range of 1172 to 6619 k Pa, as seen from Fig. 12. However, this damping behaviour was later considered to be desirable since it would reduce the high surge pressure in the dashpot as well as in the upstream portion of the valve. The high surge pressure would otherwise occur during the initial impulsive contact between the valve disk and the dashpot piston. Furthermore, as desired, this damping behaviour existed only for a short period of time. As soon as the dashpot piston passed the 3.18-mm orifice (first orifice), a significant amount of damping was imparted to the piston. The D D F values of configuration No. 2 with its 1.38-mm orifice open and the other orifice closed, were 175 to 176 for the specified cylinder pressure range. Though this damping was close to the desired range, a subsequently established requirement of a minimum orifice size of 3.18 mm to avoid orifice plugging ruled out the use of the 1.38 mm orifice.


Therefore, some supplementary tests were conducted using configurations No. 1C and 1D to obtain a stack of 3.18-mm diameter orifices that would provide the desired damping.

The damping performance of configuration No. 1C, whose adaptor contained 27 axial 'in-line' stacked orifices, was unacceptable, as seen from Fig. 13. Its maximum DDF was 40. The damping performance of this unit improved slightly when the 'in- line' stacked orifices were retightened during subsequent testing. The damping provided by configuration No. 1 D, whose adaptor contained a set of 27 stacked flip- flop orifices, was within the desired range. That is, the DDF values were within the range of 200 + l0 for the dashpot pressure range of 4900 _+ 30kPa. It is believed that this damping was obtained almost entirely by the resistance of the orifice stack alone, since the rubber 'O' ring probably sealed the annular clearance between the piston and cylinder, thereby forcing all the water to flow through the stacked orifices.

With the completion of the above tests, the objective of the developmental water tests was attained. It was subsequently recommended that the stacked flip-flop orifices should be incorporated in the piston of dashpot Configuration No. 2. This dashpot unit should be then sent to Colorado State University (CSU) for an extensive hydraulic testing.

FINAL DASHPOT WATER TEST AT CSU

The stack of 27 flip-flop orifices was incorporated in the piston of configuration No. 2. Configuration No. 2 was then installed in a full-size 406-mm prototypical check valve. This valve was then subjected to a series of hydraulic tests utilising large water flow capacities available. The main purposes of the CSU tests were:

(a) to evaluate the performance of the prototypical check valve, (b) to evaluate the performance of the dashpot configuration No. 2, and decide

upon a final dashpot design before its extensive testing in liquid sodium. The various performance requirements for the prototypical valve (including the

dashpot) during the CSU hydraulic tests were presented in a companion paper. 5 Some of those requirements are:

(1) The dashpot piston should actuate when contacted by the closing valve disk, with reverse flow equal to or greater than 1.36 m3/min. The valve disk under such conditions should be capable of closing within five seconds.

(2) During the closing of the valve disk, the damping provided by the dashpot piston to the closing valve disk should be capable of limiting surge pressures to 345 kPa or less and the maximum peak pressure to less than 1550 kPa in the test loop.

During these CSU hydraulic tests, some dashpot modifications were made to meet the specified performance requirements. The modified unit (configuration No. 2A) contained two 3-18-mm diameter radial orifices in the cylinder wall and a stack


of 27 flip-flop 3.18-mm diameter orifices in the piston (Fig. 14). This unit met all the performance requirements including the damping performance requirement stated in (2) above.

Because dashpot modifications were made at CSU, the assumption of desired DDF values of 200 + 10 became questionable. Therefore, a damping test of the modified unit (configuration No. 2A) was performed at FWEC to determine its DDF values.

Cylinder GuidePin for Installing

Flip-Flop Orifices

• y

Flip-Flop Orifices -Piston Ring

Fig. 14. Photograph showing configuration No. 2A.

DAMPING TEST IN WATER AT FWEC

The damping test at FWEC was performed after installing configuration No. 2A in the developmental water test rig shown in Figs. 9 and 10. The following conclusions were drawn from the results of this test:

(1) During the initial part of the dashpot piston stroke, when both radial orifices in the cylinder wall and the stacked orifices in the piston were open, the dashpot damping (DDF) was low. DDF values were in the range of 7 to 10 for the pressure range of 732 to 6205kPa as shown in Fig. 15. This damping was considered satisfactory for this part of the piston stroke.

(2) During the latter part of the piston stroke, when both radial orifices were

DASHPOT DEVELOPMENT TEST FOR FFTF C O L D LEG CHECK VALVE 37

2 2 0

2 0 0

180

D 1 6 0 -

D 140

F 120

I 0 0

8 0

6 0

4 0

20

0 0

o o

cz : Rodial ond stocked orifices open

o Only stacked orifices open

5) o

o °

o

r P I rT I uc I t~ Icu I I 2 3 4 5 6

DoshpotCylinder P r e s s u r e - k P o

n ] 7 x I0 3

Fig. 15. D D F versus cylinder pressure-dashpot configuration No. 2A.

closed and the stacked orifices in the piston were open, D D F values of 130 _+ 20 were experienced for the dashpot cylinder pressure range of 4900 + 30 kPa. Hence, D D F values of 130 _+ 20 were established to be the new dashpot damping standard as compared to the original range of 200 _+ 10.

To summarise, the dashpot for the FFTF Cold Leg Check Valve has been developed by water testing two basic configurations and their modifications. Upon completion of this test programme, a prototypical unit was fabricated. This latter unit was subjected to acceptance tests in air and freon and a number of tests in liquid sodium. The performance of the prototypical design during these tests was concluded to be satisfactory.

APPENDIX

Dashpot damping Jactor (DDF) derivation and calculation The flow rate of the fluid out of the cylinder cavity for an annular dashpot

configuration can be given by: 6

W = CaA.x / /~pp ( 1 )


The flow rate given by eqn. (1) can also be related to the displacement of the dashpot piston, in the following manner:

7~ W = 4DZPr (2)

Utilising eqns. (1) and (2), the fact that A a = 7rDt for t/D ~ 1 in an annular dashpot design; and DDF = 1/C 2, DDF can be expressed as:

DDF - 32pgct: (3) pOZt ,2

where: DDF = a dimensionless parameter characterising hydraulic resistance of dashpot piston to the closing simulated or actual valve disk, p = pressure head in the dashpot cylinder, gc = gravitational constant, t = annular clearance between piston and cylinder, D = dashpot cylinder internal diameter, t, = dashpot piston velocity and p = density of test fluid.

For annular dashpot configurations, eqn. (3) was used to calculate the DDF values by experimentally measuring the 'p' and 'v' and inserting the measured values of 't ' and 'D'. This equation was also used for non-annular configurations. The values of 'p' and 't" were experimentally determined. Values for 't ' and 'D', which define an equivalent annular dashpot, namely dashpot configuration No. 1, were inserted. Hence the non-annular design had the same damping characteristics as the equivalent dashpot configuration No. 1 when both were assumed to be operating under the same 'p' and 'r ' conditions.

ACKNOWLEDGEMENTS

The authors would like to thank I. Berman for his review of the paper and helpful comments; G. Rabe for his recommendations used to redesign the dashpots; J. Apice and M. McKeeby for their graphical work; Nancy Marshall for typing the manuscript; Westinghouse Advanced Reactor Division, Pittsburgh, Pennsylvania, who supported the work and the FWEC for permission to publish this paper.

REFERENCES

1. POOL, E. B., PORW1T, A. J. and CARLTON, J. L. Prediction of Surge Pressure from Check Valves for Nuclear Loops, ASME Paper Number 62-WA-219, presented at the Winter Annual Meeting, New York, New York, November 25-30 (1962).

2. POOL, E. B. Minimization oJ Surge Pressure Jrom Check Valves Jor Nuclear Loops, ASME Paper Number 62-WA-220, presented at the Winter Annual Meeting, New York, New York, November 25- 30 (1962).


3. IMANAKA, N., AOK1, T. and YAMANARI, K. Operating Experience and Design Criteria of Sodium Valves in Japan, Summary Report, International Working Group of Fast Reactors Specialist Meeting on Operating Experience and Design Criteria of Sodium Valves, U.S.A. ERDA, Technical Information Center (1974) pp. 262 3.

4. ZEMANICK, P. P. Sodium Valve Analysis Criteria and Methods, Summary Report, International Working Group of Fast Reactors Specialist Meeting on Operating Experience and Design Criteria of Sodium Valves, U.S.A. ERDA, Technical Information Center (1974) pp. 262 3.

5. KANE, R. S. and CHO, S. M. Hydraulic performance of tilting-disk check valve, Journal of the Hydraulics Division, Proceedings o[ the American Society oJ Cit, il Engineers, 102 (HY1) (1976).

6. GIBSON, A. H. Hydraulics and its Applications, fifth edition, Constable and Company Ltd, London (1952) pp. 107 9.

dashpot development test for fftf cold leg check valve

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