Timed-dose and drip systems: reading the dosing pattern instead of guessing

On a timed-dose system the pump starts either when the timer triggers it or when the water reaches the high float, and most of the time it is the timer. A low float keeps it from running dry. The timer is one of two kinds:

• A 24-hour timer runs the pump at set times of day, for a set number of minutes each time. Spray systems that pump overnight usually work this way.
• An interval timer (also called a repeat-cycle or dose timer) runs the pump on for a set time, off for a set time, around the clock. Two minutes on, ninety minutes off, say.

Either way the point is the same: the field works best with small, even doses spread across the day rather than a flood whenever the house happens to drain.

That makes the timer settings matter in a way a float never did, and it makes them hard to get right without seeing what the system is actually doing.

The three numbers that matter

A timed-dose system has three things to balance:

• How much water the house sends to the tank each day. This varies with laundry day, guests, and season.
• How much each dose moves to the field. Set by the run time per dose and the pump’s flow rate, less whatever is sent back to the tank through a return line.
• How many doses per day. On a 24-hour timer, the number of start times you have set. On an interval timer, the day divided by the on time plus the off time.

Set the timer too high and the field gets water faster than it can soak it in. Wet spots on a drip field and seepage at the toe of a mound are the signs. Set it too low and the tank fills faster than the schedule empties it. Eventually the high float starts the pump itself, and that run is bigger than a scheduled dose, so the field gets a gulp instead of a sip. Keep it up and the alarm float trips. A good schedule gives the field small, even doses that add up to what the house produces, and the floats never have to step in.

The return valve

Drip systems have a return line from the pump back to the tank with a manual valve on it. Part of each dose goes back through it instead of out to the field. The installer sets the valve to put the field at the right pressure and keep the pump in its efficient range, and it also lets a service tech flush the filter and laterals by opening it wide. Opening it sends more of the dose back to the tank and less to the field; closing it does the reverse, though with pressure-compensating emitters the field dose barely changes until the pressure falls out of their range. People adjust that valve to fix a wet spot or a slow tank and then forget which way they turned it, and the system quietly runs off its intended dose from then on.

Fields with more than one zone dose them in rotation, so run time per dose has to be compared zone by zone.

Why guessing does not work

A timer change takes days to show its effect. If you drop a start time or lengthen the off interval to dry out a wet spot, the tank level rises slowly and the first sign that you went too far is the high float starting the pump, or an alarm, a week later. If you shorten it, the wet spot may or may not improve, and rain confuses the picture. Most people make one change, wait, cannot tell what happened, and leave it.

What you need is to see the system’s own numbers before and after:

• Doses per day actually delivered. On a timer this should be steady. If the count is higher than the schedule, the high float is starting extra runs, which means the schedule is not keeping up. If it is lower, the tank is running short between doses and the timer is being held off, which means the schedule is generous or the house is using less water than it was designed for.
• Run time per dose. Should match the on time you set. If actual runs are shorter, the pump is hitting the low float before the timer ends, which means the tank is running short and the schedule is generous. If they are the full length every time, the tank is keeping up or more.
• Real power per dose. A pump pushing against a clogging filter or a field that is saturating works against more head, and a pump whose return valve has been opened wide works against less. Both show up as a shift in power from the pump’s own normal.

With those three, a timer change becomes an experiment with a result instead of a guess with a wait.

Rain and sprinklers

The hardest thing to tell on any septic system is whether a rise in water is coming from the house or from outside. Rain into a leaky riser, a sprinkler zone over the tank, or groundwater seeping in all look the same to the pump. On a timed-dose system they look like a schedule that was fine in August and overwhelmed in October.

The dosing record narrows it down: if the extra float-started runs line up with rainy days and not with laundry days, you have an infiltration problem, not a timer problem. A water-level sensor in the tank would show all of this directly. But the pump runs and the float triggers already carry a rough version of the same information: how fast the tank is refilling between doses, and when it gets ahead of the schedule. For most systems that is enough to tell whether water from outside is a big enough problem to be worth fixing.

Where Septic Brain fits

Septic Brain records every dose on a timed system as it happens: when it ran, for how long, and the real power while it did. That gives you doses per day, run time per dose, and a power trend, from the control panel, with nothing in the tank. Make a timer or return-valve change, look at the week before and the week after, and know whether it worked. If your septic pro set the schedule, share the view with them so they can see the same thing.