Dynamic Per - Check Valve
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VALVOLA CORPORATION THANE -421 302 NO. :- VC/ DCV / 6800 / 00 DATE :- 28.01.2013 PAGE :- 1 OF 3 Dynamic Characteris tics of Check Valve Need of Check Valve 1) To prevent rever se f low. 2) To hold pre ssur e in the pipe line . 3) To provide wate r ha mmer mitigation. 4) For posit ive di splaceme nt pump s operation. 5) To prevent, Para llel pumps rotating in reverse. 6) To stop a pipe or tank empty ing. Selection of Check Valve There are ma ny tools availa ble for selecti on of check valv es. Main criteria in volve in selection of check valve are:- 1) Non- Slamming Cha ract eris tics . 2) Head loss Characte ris tic s. 3) Operating Cost. 4) Ma intena nc e Cost. 5) Cont rollabil ity . 6) La yi ng Le ngth. Dynamics Characteristics of Check Valve Check Valve slam occurs after pump stop and the system flow reverses back towards the pump before the check valve is fully closed. The reverse flow causes the check valve to close rapidly through the remaining portion of its travel. The reverse flow is then stopped by the closed valve causing water hammer in the line. Prepared By : Approved By :
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Transcript of Dynamic Per - Check Valve
8/13/2019 Dynamic Per - Check Valve
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VALVOLA CORPORATIONTHANE -421 302
NO. :- VC/ DCV / 6800 / 00
DATE :- 28.01.2013
PAGE :- 1 OF 3
Dynamic Characteristics of Check Valve
Need of Check Valve
1) To prevent reverse flow.
2) To hold pressure in the pipeline.
3) To provide water hammer mitigation.
4) For positive displacement pumps operation.
5) To prevent, Parallel pumps rotating in reverse.6) To stop a pipe or tank emptying.
Selection of Check Valve
There are many tools available for selection of check valves. Main criteria involve in selection of
check valve are:-
1) Non-Slamming Characteristics.
2) Head loss Characteristics.
3) Operating Cost.
4) Maintenance Cost.
5) Controllability.
6) Laying Length.
Dynamics Characteristics of Check Valve
Check Valve slam occurs after pump stop and the system flow reverses back towards the pump
before the check valve is fully closed. The reverse flow causes the check valve to close rapidly through
the remaining portion of its travel. The reverse flow is then stopped by the closed valve causing water
hammer in the line.
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VALVOLA CORPORATIONTHANE -421 302
NO. :- VC/ DCV / 6800 / 00
DATE :- 28.01.2013
PAGE :- 2 OF 3
Water hammer & related problem like surge pressure, vibration, shocks can leads serious
consequences in the system.
Dynamic Characteristic is a term use to describe, how check valve perform under various
situations and is normally illustrated by the means of a graph. All self acting check valves allow some
degree of reverse flow prior to shut down situation. Thus, sudden reductions of this back flow to zero
yield a surge pressure. The graphs plotted between reverse velocities against declaration describe the
Dynamic Characteristic of check valve.
To Prevent Slam, Check Valve must be either of the following
1) Check Valve Close quickly before reverse flow occurs:-
The disc should have Low Inertia and Friction.
The travel of the disc should be short.
Spring should be used to close the disc.
2) Check Valve Close very slowly once reverse flow developed
For this valves should be equipped with the external device like dashpot and the pump
must be capable of withstand some backspin.
The reverse velocity can be converted directly into water hammer pressure using the
equation:-
Where, h = Pressure Rise, ft of water.(m)
a = Wave Velocity, ft/sec. (m/s)v = reverse velocity, ft / sec. (m/s).
g = 32.2 ft / sce (m/s ).
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VALVOLA CORPORATIONTHANE -421 302
NO. :- VC/ DCV / 6800 / 00
DATE :- 28.01.2013
PAGE :- 3 OF 4
Example
Expected transient condition for 6’’ pipeline:-
Fluid – Water
System Deceleration – 5 m/s2
Line Pressure - 10 Bar
Rated System pressure – 16 Bar
Pressure Wave – 1000 m/s.
Density of Water – 1000 Kg / m3.
Valvola”Series-6800” = 0.29 m/sec
Pressure Rise (h) = Density of Water X Pressure Wave X Reverse Velocity
= 1000 kg/m3
X 1000 m/s X 0.29 m/s
= 290 kN / m
2
(kPa)h = 2.9 Bar
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VALVOLA CORPORATIONTHANE -421 302
NO. :- VC/ DCV / 6800 / 00
DATE :- 28.01.2013
PAGE :- 3 OF 4
Dynamic Performance Graph for Check Valve [1]
On Graph, locate 5 m/s2
on X- Axis, move vertically, and then read left on Y-Axis to determine the
velocity. For 5 m/s2
Deceleration, velocity shall be 0.29 m/s.
Referances :- [1] – Utah state Water Research Laboratory.
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