Water Hammer -
Water Hammer -
(OP)
Hi,
I have calculated the water hammer effect, and I have 500 psi (delta P), more my normal operation at the inlet valve (550 psig), my pressure can increase to 950 psig in my worst case. Also, I have calculated my closing time and I got 7 sec.
(with Joukowski's equations).
If my understanding is good, even if my closing time is longer than 7 sec, I will have the water hammer effect, but I reduce the pression reached.
MY QUESTIONS : How to calculate the pressure with different closing time, because in my case, I'm looking to put a closing time to respect my pipe spec.
Thank you,
Ken
I have already read :
http://www.eng-tips.com/viewthread.cfm?qid=168831
I have calculated the water hammer effect, and I have 500 psi (delta P), more my normal operation at the inlet valve (550 psig), my pressure can increase to 950 psig in my worst case. Also, I have calculated my closing time and I got 7 sec.
(with Joukowski's equations).
If my understanding is good, even if my closing time is longer than 7 sec, I will have the water hammer effect, but I reduce the pression reached.
MY QUESTIONS : How to calculate the pressure with different closing time, because in my case, I'm looking to put a closing time to respect my pipe spec.
Thank you,
Ken
I have already read :
http://www.eng-tips.com/viewthread.cfm?qid=168831





RE: Water Hammer -
Drugs are bad.
RE: Water Hammer -
Also what is rho*c, initial velocity and length of piping?
RE: Water Hammer -
RE: Water Hammer -
4 000 m = length
700 m³/hr = flow.
RE: Water Hammer -
Solve Joukowski's equation for velocity, given the maximum pressure increase you want to have. Consider that to be a maximum change in velocity that limits the surge pressure increase to your maximum desired value. Do not change the fluid's velocity in the pipeline by more than that amount during the time it takes for the pressure wave to arrive at the end of the pipeline.
For best response, take care of the valve selection by choosing a valve with a linear relationship of change in velocity (or flowrate) across the valve to the valve's closing time. That is usually accomplished by selecting a valve with a linear relationship between flowrate and %Open and using an actuator with a linear relationship between its position and travel time. Ball and gate valves do not have linear characteristics of change in flow rate vs Position and almost all of the change in flowrate will occur during the last 20% of the closing operation. Therefore if you are using a ball or gate or similar flow pattern valve, and you set a closing time for the actuator, use 20% of that actuator travel time for calculation and comparison with the answer you get from the Joukowski equation.
http://virtualpipeline.spaces.msn.com
RE: Water Hammer -
http://virtualpipeline.spaces.msn.com
RE: Water Hammer -
1 You should use a water hammer program -one that uses the method of characteristics.
2-Obtain from the valve vendor(S)/valve operator, the valve operating characteristics-flow area vs. valve position or better yet valve Cv vs position. AND valve position vs time.
With the above AND the boundary conditions for the system you should be able to select the proper valve/operator to limit you pressure surge.
RE: Water Hammer -
I'm sorry, I have forgotten to mention that is a ON/OFF valve...
RE: Water Hammer -
http://virtualpipeline.spaces.msn.com
RE: Water Hammer -
RE: Water Hammer -
http://virtualpipeline.spaces.msn.com
RE: Water Hammer -
RE: Water Hammer -
Gases, if present, may markedly reduce sonic velocities.
Also a visit to
http://www.flowguardusa.com/docs/Article_Surge.pdf
may be of some help.
RE: Water Hammer -
Regards