Calc Hydraulic Hammer Downstream of Control Valve

[rppearso]

how do you calculate hydraulic hammer downstream of a control valve. Perrys section 6-44 talks about valve closure time to prevent surge but what about valve opening time to prevent surge on a downstream elbow. You could use F=ma but what would your mass be, would it be the entire mass of the fluid all the way to the point of a pressure generating device (ie a pump or pressurized gas blanket)? Would the valve opening time be an iterative calculation with the first slug of liquid being calculated using F=ma and subsequent calculations be made using pulsation calculations for an already packed line? My guess would be that the worse surge would be the initian F=ma surge and once the line was packed there would be no concern for hydraulic surge. I am also thinking about just putting in a small bypass to liquid pack the line before the main valve is open but still would like to back it up with calcs.

 

[Navin A S]

The calculation of hammer downstream of a control valve is best done using a one-dimensional, unsteady flow model. The mass in the equation F=ma needs to be the mass of the fluid moving through the line, and this can be calculated by solving the equations of motion that describe the flow. The valve opening time can then be determined from the pressure wave propagation in the line. It may be necessary to use an iterative approach to first calculate the initial slug of liquid, and then use pulsation calculations for the already packed line. It is also possible to use a bypass line to liquid pack the line before the main valve is opened, which could further reduce the risk of surge.

 

[oswaler]

I would approach this problem by first understanding the properties of the fluid and the system in question. This would include factors such as the fluid's density, velocity, and pressure, as well as the dimensions and design of the control valve and downstream elbow.

To calculate the hydraulic hammer downstream of a control valve, I would use principles of fluid mechanics and apply them to the specific system. This would involve using equations such as the Bernoulli equation and the continuity equation to determine the pressure and velocity changes in the fluid as it flows through the system.

The mass to be used in the calculation would depend on the specific scenario and the desired level of accuracy. In some cases, it may be appropriate to use the entire mass of the fluid in the system, while in others, it may be more accurate to consider only a portion of the fluid that is directly affected by the control valve and downstream elbow.

The valve opening time can also be calculated using fluid mechanics principles, taking into account factors such as the inertia of the fluid and the rate at which the valve opens. This may involve an iterative calculation process, as you mentioned, to account for the initial surge and subsequent pulsations in the system.

In terms of preventing surge on a downstream elbow, there are various methods that can be used, including the use of bypass lines or surge tanks. These can also be analyzed and designed using fluid mechanics principles to ensure their effectiveness in preventing surge.

Overall, as a scientist, I would use a combination of theoretical calculations and experimental data to accurately predict and prevent hydraulic hammer downstream of a control valve. This would involve a thorough understanding of the system and the fluid properties, as well as the application of established principles and equations from fluid mechanics.