"Hydraulic Lock"

[Groundwood]

I am wondering what causes a "hydraulic lock" in piping systems, if there is such a beast? More specifically, I have a multiple fed header in which the flow for one out of the 6 feed lines appears to be choked off. This line is the furthest upstream to feed the header. We have checked for obstructions in the piping, checked valves and calibrated flow meters, but there still appears to be a strange reduction in flow. Any suggestions?

 

[CRG]

Are there significant elevations, when compared to the pump discharge head, in the piping system? If so, your pipe may be air bound such that the fluid cannot be pushed to the higher elevation with the available pressure. In other words, the static head of the vertical pipe length is greater than the head available to push the fluid up to the top. Once air is removed from the system, the fluid on the downstream side of the elevation will cancel out the required static head on the upstream side.

If so, you need to get the air out of the problem circuit. Methods may include filling the problem circuit with fluid. Shut the other five feed lines to get the required head for circulating the problem line, and then open the other lines. Pressuring the system and bleeding the air from the problem circuit. Etc
.

 

[cmsm]

If the fluid velocity pressure is high with respect to the total pressure then the fluid will impact the end to the manifold and push hardest on the last branch. The first branch will get the least, especially if the last branch can take all the flow. Kind like a fire hose against a flat plate.

 

[25362]

Manifolds tend to perform in a strange manner in respect of distribution on takeoff or feeding lines, sometimes contravening conventional wisdom. Perry VI, in its Chapter 5 on "mechanics of fluids and particles", gives explanations of maldistribution concerning manifolds, much in line with cmsm comments, and depending on the relative diameters of manifold and feed or takeoff lines.