When you look at a sand filter or a water softener, you see only the tank and the control head. But inside the tank is a small part the performance of the whole system depends on: the internal distribution system. It is the part that spreads water over the media bed and keeps sand or resin from escaping with the water.
What is an internal distribution system?
It is the set of components installed inside the filter tank (usually an FRP fiberglass tank) to guide water through the media correctly. It typically consists of:
- Upper diffuser: spreads the incoming water over the top of the media bed.
- Lower diffuser: collects the filtered water from the bottom of the tank and holds back the media grains.
- Hub & laterals: slotted arms extending from a central hub at the bottom of the tank, used in larger tanks to cover the whole base area.
- Riser tube: connects the control head to the lower diffuser.
Why does it matter?
- Distributing water over the media: so the sand, carbon or resin bed works across its entire area.
- Retaining the media: the diffuser slots let water through and stop the media from escaping.
- Supporting backwash: helps spread backwash water through the bed to clean it.
Top-mount and side-mount
Distribution systems come in two configurations: top-mount, where the control head sits on the tank’s top opening and the riser tube runs down to the base, and side-mount, where the piping connects at the side of the tank, which is common in large tanks and plants. The tank and control head design determine which type you need.
Signs the distribution system has failed
- Sand or resin beads showing up in the water after the filter or at the faucets.
- Lower softening or filtration efficiency even though the control head settings are correct.
- Repeated clogging of cartridges or appliances downstream of the filter.
- A change or fluctuation in water pressure after backwash.
In these cases the tank is opened, the diffuser and laterals are inspected, and anything broken or blocked is replaced with a part of the matching size.
FRP tank accessories
Besides distribution systems, fiberglass tanks sometimes need closures and opening reducers to adapt the tank opening to the control head, as well as air-release valves to vent air trapped inside the tank.
How do you choose the right part?
- Know the tank’s diameter, height and opening size.
- Identify the type of control head (such as RUNXIN heads and others) and whether it is top-mount or side-mount.
- Send a photo of the old distributor if you have it; it is the fastest way to match the part.
Available at TNT
We supply internal distribution systems for media filters and softeners for 130 JOD in various sizes, along with FRP tank accessories and on-site inspection and replacement service. Learn more about water softeners and treating hard water, message us on WhatsApp with a photo of your tank so we can identify what you need, or request a maintenance service.
