Where the controller’s probes should sample the tower water, how to plumb the sample line so they read true, and how to plumb the bleed valve and the make-up meter.
The sample line and bleed are pressurized. Isolate and depressurize before opening any fitting or removing a probe. See Pressurized Systems and Isolating Equipment.
flowchart LR
HI["Pump discharge<br/>(high pressure)"] --> V1["Hand valve"] --> ST["Strainer"] --> U1["Union"] --> FC["Flow cell / probes<br/>flow bottom to top"] --> U2["Union"] --> V2["Hand valve"] --> LO["Pump suction or basin<br/>(low pressure)"]
SYS["System side"] --> MV["Manual throttling valve"] --> BST["Strainer"] --> SV["Bleed solenoid valve"] --> DR["Drain"]
- Sample where the water is mixed, before the chemical goes in. Take the sample downstream of the recirculating pumps and upstream of every chemical injection point, so the probes see system water, not a plume of fresh chemical.
- Drive the flow with a pressure difference. Take the sample from a high-pressure point (pump discharge) and return it to a low-pressure point (pump suction or the basin). Without a real difference in pressure, nothing flows past the probes.
- Keep the flow within the flow cell’s range. Too little and readings lag or drift; too much and probes wear or bubbles form. Pulsafeeder specifies 1–5 gpm (3.8–19 L/min) for its flow assembly; check the flow cell or probe manufacturer for yours.
- Flow from bottom to top through the flow cell. It carries bubbles out, keeps the electrodes covered, and lets a flow switch in the cell work properly.
- Keep the electrodes submerged at all times, including when flow stops.
- Fit a strainer upstream of the flow cell to keep debris off the probes.
- Fit hand valves on both sides, for isolating, throttling the flow, and removing probes and cleaning the strainer — and unions on the inlet and outlet so the assembly can come out.
- Fit a flow switch in the sample line, and use it as an interlock on every mode: with no flow, the probes are reading stagnant water.
- Tighten NPT fittings hand tight, then about a half turn on plastic flow cells. Over-tightening cracks plastic threads.
- Fit a manual valve on the system side of the solenoid valve. It isolates the solenoid for service and throttles the bleed rate. Throttle it so a bleed takes several minutes to bring conductivity down — a bleed that is too fast overshoots and chatters.
- Check the solenoid valve’s minimum pressure differential. Most general-purpose solenoid valves need about 7–15 psi (0.5–1 bar) across them to close. Where the bleed line has less, fit a zero-differential (direct-acting) valve.
- Fit a strainer upstream of the solenoid — debris is the most common reason a bleed valve sticks open.
- Size the drain for the bleed flow, with an air gap as your plumbing code requires.
- Set a limit alarm on the bleed mode, so a valve that is stuck, clogged, or throttled shut raises an alarm. See Setpoint Control.
- Install it horizontally, with its face up, unless the manufacturer says otherwise.
- Give it straight pipe: at least 12 pipe diameters upstream and 6 diameters downstream, all of the same size as the meter.
- Put it on the make-up line only, after any branch that does not feed the tower, so it counts only water that goes into the system.
- Wire its pulse output to the controller and set its K-factor. See Meters and Switches and Pulse and Contact Inputs.
- Pulsafeeder, Technical Reference Guide — 9300/9500 Series Cooling Tower Controller, 72-900-29 Rev D, §2.1–2.2 Location and Installation Notes — the sample-line, bleed, and water meter guidance is adapted from it. PDF