I am running tow different scenarios. A pump shutdown with a pump check valve and a pump shutdown and startup with a pipe check valve and the check valve at the pipe closes slower than the check valve at the pump every time. I know that Hammer models the pipe check valve at the midpoint in the pipe so I would have assumed that the pipe check valve would be the first to close since both types of valves are programmed to close at the first detection of reverse flow. I tried to model the pump shutdown pattern as similar to the ramp down driven by the inertia.
But, no matter how I change the pattern for the pump shutdown and startup, the check valve at the pipe always closes after the pump speed has reached zero. So, for example under my first pattern, the pump would reach a speed of zero after 12 seconds and the check valve would close at 12.6 When I change the pattern to have the pump speed reach zero after 8 seconds now the check valve closes at 11.7 s. But when I use a pump check valve, the check valve closes after 11 s when the pump speed is still 190 rpm.
Any idea what's going on?
The following link has information on check valves and how they are modeled in HAMMER: Modeling Reference - Check Valves.
With the check valve on the pump and the check valve associated with a pipe, it is assumed to close instantly when reverse flow is detected. It is possible that the pump will stay on for another time step, but it should stop flowing after the check valve is closed.
There is a check valve element that you can include in a model that will allow you some control over how fast the valve opens and closes. This link above as information on that.
If that doesn't help, we will likely need to see a copy of the model files.
I have read that, thank you. I'm not sure I am asking my question correctly.
When I create a pump pattern the pipe check valve always closes after the pump has reached 0 rpm. Whether it takes 7 seconds to ramp down of 13 seconds, it doesn't matter, the pipe check valve closes right after.
When I model no check valve and let Hammer determine the ramp down pattern based on pump and motor inertia it takes 13 s to fully ramp down (hence why I chose the above pattern on 13 seconds to ramp down).
When I model a check valve and let Hammer determine the ramp down pattern based on pump motor and inertia it takes 6 seconds for the check valve to close. This indicates that reverse flow is detected before the pump has fully ramped down to 0 rpm.
So, why is my pipe check valve indicating that closure occurs after the pump has fully ramped down?
Would you be able to send the model files to us? That might help to better see if there is some other factor coming into play here.