Pressure jumps 10 PSI when water feature (slide) is being used

[poolgal13]

We opened our pool a few weeks ago ourselves. DE filter was manually cleaned. Everything was working fine. Today, we were vacuuming up all the maple helicopters, dirt, etc. I happened to remember that we had not opened the valve that controls water flow in the pipe that leads to our pool slide. We opened up, and the slide had water. I happened to look at the filter pressure shortly after, and the PSI was up 10 points. I assumed I needed to backwash since I had vacuumed. After backwashing it was still high. My husband turned off the valve that controls the piping to the slide, and the pressure dropped to normal. What could cause this?

[SunnyOptimism]

How is the water slide plumbed into the pressure side of the pump? Can you attach a picture (use a photosharing service like Picasa or Photobucket and just copy & paste in the IMG link)?

Opening up another pipe for water to flow through should drop the system pressure or, at the very least, not raise it. The only circumstance I can think of in my own pool is that I have an attached spa with a single return to it so that the spa can spill over into the pool. There is a three-way valve that splits the flow between the single spa wall return and the three pool wall returns. If I try to push all of my return water through that single spa wall return, I can easily jack up the system pressure by 10psi.

Also, as you open and clean up all the spring time "garbage" that floats into your pool, you'll need to backwash more frequently than during the height of the swim season when there's less debris.

[poolgal13]

Strange! I went out to take a picture like you asked and tried one more time to open the valve just enough until water came down the slide like normal, and VOILA! the pressure on the tank is fine. If I open the valve on the pipe all the way (basically turn the handle all the way) the pressure goes up. I'm guessing that in previous years when the pool company opened up our pool for us, they probably never had the pipe opened all the way. I think it's all good for now, but if something weird happens, then I will re-post.

[SunnyOptimism]

Strange! I went out to take a picture like you asked and tried one more time to open the valve just enough until water came down the slide like normal, and VOILA! the pressure on the tank is fine. If I open the valve on the pipe all the way (basically turn the handle all the way) the pressure goes up. I'm guessing that in previous years when the pool company opened up our pool for us, they probably never had the pipe opened all the way. I think it's all good for now, but if something weird happens, then I will re-post.

That is a bit weird.

Which do you think has the shorter pipe run length, the pool returns or the water slide? How many eyeball returns are there in the pool? Do you know the PVC pipe diameters for the pool returns versus the slide?

I'm trying to understand why your pump seems to be forcing more water to the slide than the pool returns. Water flow, like electricity, tries to follow the path of least resistance. So, adding more parallel streams of water to the pressure side of your plumbing, ie, opening the pool slide valve, should decrease your system pressure not increase it. As I stated in my first reply, the only thing that would cause what you're seeing is a three-way valve where turning on the slide fully also diverts water away from your pool returns. There are other even less likely scenarios (like having a variable-flow water pump) but I suspect that's not the case.

Pictures would definitely help sort out this mystery...but if you're happy with what got, enjoy the water slide!!