The same valve, minus one circuit
A filter valve runs the sediment-vessel cycle: service, backwash, fast rinse. A softener valve runs the same three positions plus the brine circuit (brine draw with slow rinse, and brine-tank refill), with the venturi injector and refill control built into the valve body. Outwardly the two are near twins from the same product families; internally the softener valve carries the extra ports, injector assembly and cycle logic.
That one-way relationship sets the compatibility rule. A softener valve on a plain filter vessel can work: its brine positions idle unused (some models configure them out), and you have merely paid for hardware doing nothing. A filter valve on a softener cannot work. There is no brine draw, so the resin regenerates with nothing and exhausts once. The softener becomes an expensive vessel of saturated resin delivering hard water while "regenerating" on schedule. The failure is silent: every cycle runs, water flows, nothing is soft.
How to tell what you are holding
- Ports: the softener valve has a brine port (usually a small barbed or threaded connection for the brine line) that the filter valve lacks. That nipple is the giveaway.
- Codes: in Runxin's old scheme, softener valve families and filter valve families are separate series; in the new five-digit convention the first digit carries it: 5 for filter valves, 6 for softener valves (7 and 9 for the specialised series). The code reference tool decodes any code either way.
- Controller menus: softener controllers expose brine and salt settings; filter controllers only backwash timing.
Specifying the right one — and the settings that follow
The choice itself is trivial once stated: media-only vessels (sand, glass, carbon, catalytic) take filter valves; ion-exchange vessels take softener valves. The traps are adjacent:
- Carbon and catalytic media vessels are filters, whatever their softener-like appearance in the plant room. No brine, filter valve. (The one exception worth knowing: manganese greensand regenerated with permanganate uses softener-style hardware for the regenerant draw. That is a specialised design, not a default.)
- A replacement valve must match the vessel and internals, not just the old valve's role: vessel thread, riser diameter, and, for softeners, injector size matched to resin volume. A mismatched injector regenerates poorly and imitates resin failure.
- Second-hand and reassigned equipment is where most wrong-valve installations happen: a "spare valve from the old filter" pressed onto a softener, or a softener valve inherited by a carbon vessel with its brine cycle left active. The latter only wastes water on a phantom brine draw, but it wastes it every cycle.
- Settings complete the match: a correctly chosen softener valve still needs its resin volume, salt dose (refill time) and hardness programmed; a filter valve its backwash interval and duration per the media. The valve is only as correct as its configuration.
Rule of thumb: brine circuit for resin, no brine circuit for media. Check the brine port or the code's first digit (5 filter, 6 softener) before it goes on the vessel. If a softener "regenerates perfectly" yet delivers hard water, first check whether the valve on it can draw brine at all.