Sand Filter issue

[Savage1ZA]

Hi,

I have a 1.1kW pump on a ~70kL pool, with some weird thing I can't seem to place.

- Suction line remains fine throughout, kreepy runs, no suction leaks (pressure tested), no problems here what so ever.
- When the pump runs on recirculate, everything runs absolutely fine, no problems.
- When the pump runs on filter:
- I always get an "initial" burst of sand into the bath, which stops after a minute or so;
- I always get strong pressure at the start, with water returning back to the pool under a rather high pressure (granted, and I know, I can't expect as strong pressure as on recirculate mode, but that's not what this is about);
- Over time (an hour or so), the pressure of the water returning back to the pool will drastically reduce (I'd say < 30% of what it was initially);
- Turning the pump off for a while, and back on, the process repeats itself.

Thoughts, ideas?

[Teapot1]

You don't need high pressure at all, you need good flow. My pool is designed and runs at 0.5PSI but with the correct flow.
High pressure is just friction that robs you of flow and costs a lot in electricity.
Sadly the pool industry just cannot get to grips with the idea but give them another 10 years or so

[Savage1ZA]

Yea, sorry mind my terminology.

Pressure = flow. The flow reduces, drastically.

[Teapot1]

OK, difficult to diagnose from my PC but two of the usual culprits are a damaged lateral in the sand filter and/or damaged spider gasket in the multiport.
When was the filter last serviced?
What size (dia) is the filter?

[Savage1ZA]

Multiport is brand new, including the gasket.

Sand Filter is also brand new (120 liter filter), but the sand was recently replaced (by contractors, that did it with the utmost care - and I mean that sarcastically). I am not against the idea that a lateral could be damaged. I guess I'll have to just bite the bullet and take the sand out again.

ty for advice.

[Teapot1]

Sounds like it, normally the laterals have a bit of give in them when new, they get brittle with age and chlorine. the filter should be half full of water the lessen the drop of the sand into the laterals.
If you are taking out the sand, consider re filling with Dryden Aqua's AFM ng media, the best you can get and it removes lots more than sand.
https://www.drydenaqua.com/afm/afm-ng