How to adjust a water pressure switch: the order of work
A pressure switch has two nuts: the large one moves both set points (cut-in and cut-out) together, the small one changes only the differential between them. The order is: small nut to maximum differential, large nut to set cut-in, then small nut back down to the cut-out you want. That is the Italtecnica PM/5 manual procedure, and most water switches follow the same logic. Not all of them, though, as the table below shows.
A water pressure switch is a mechanical switch on the hydraulic fitting of a pump station that starts and stops the pump by pressure. You set it at installation, after replacing the pressure tank, and when system pressure has drifted.
What you need before you start
- A pressure gauge. The scale on the switch is only a hint. Manufacturers say to calibrate against a reference gauge.
- Power off. Mains voltage sits under the cover. Condor states this in its setting guide.
- The data sheet for your switch. Range, minimum and maximum differential and the turning direction depend on the model. If a number is not in the data sheet, do not rely on memory or forums.
- A drain tap or an open outlet, so you can drop pressure below the cut-in point quickly.
Step-by-step adjustment
- Switch off the power and remove the cover. You will see two springs with nuts: the large one (range) and the small one (differential).
- Turn the small nut (differential) to the maximum allowed by the data sheet.
- Use the large nut (range) to set the cut-in pressure. Clockwise usually raises the pressure, counter-clockwise lowers it, but check the "+" and "-" marks on your model.
- Restore power and open an outlet so pressure falls. Watch the gauge: the pump should start at your cut-in point.
- Close the outlet and let pressure rise. Note the pressure at which the pump stops.
- If cut-out is too high, back off the small nut a little (reduce the differential) and repeat the cycle until it lands where you want.
- Run 2-3 full start-stop cycles and confirm the points do not wander.
Do not turn a nut more than 2-3 turns at a time, or you will overshoot. That is our habit, not a manual requirement.
The nuts: what the large one does and what the small one does
The large nut shifts the whole range, the small one stretches or squeezes the differential. Condor puts it this way: when the main spring is adjusted, cut-in and cut-out change proportionally, so the differential stays the same. To widen the gap you use the differential screw.
| Adjustment | Effect on pressure |
|---|---|
| Large nut (range) | Cut-in and cut-out move together, differential unchanged |
| Small nut (differential), Italtecnica PM/5 | Per the manual, set cut-in with maximum differential, then reduce the differential to set cut-out |
| Differential screw, Condor MDR 1, 11, 2, 21 | Cut-out changes, cut-in stays |
| Differential screw, other Condor types | Cut-in changes, cut-out stays |
This is where people get caught: on two neighbouring switches from one brand the small screw can move different points. We always read the model marking and the data sheet before touching anything.
Example: Italtecnica PM/5
The PM/5 is the common switch for household and small pump stations. Per the Italtecnica manual: range 1-5 bar, factory setting 1.4-2.8 bar, differential 0.6-2.3 bar, 250 V, 16 A, IP44. The PM/12 version: 3-12 bar, factory 5-7 bar, differential 1.5-5 bar.
- Target 2.0 / 3.5 bar. The differential is 1.5 bar, inside the 0.6-2.3 bar window of the PM/5. Small nut to maximum, large nut to 2.0 bar cut-in, then raise cut-out to 3.5 bar with the small nut.
- Target 1.0 / 5.0 bar. A 4 bar differential exceeds the PM/5 limit of 2.3 bar, so this switch cannot do it. You need a PM/12 or a different control scheme. The setting diagram in the manual shows which pairs are allowed.
This is arithmetic, not a recommendation: the right pressure depends on pump head, building height and what the appliances need. Cut-out must stay below the maximum that the pump, pipes and fittings can take; check that separately.
Accumulator precharge and the switch
Air pressure in an empty pressure tank should sit slightly below the cut-in pressure. A guideline from a switch supplier (Boshart): about 2 PSI (roughly 0.14 bar) below cut-in, with at least a 2-5 PSI buffer between precharge and cut-in. Measure with the tank drained of water. Check the plate on your tank for exact values.
If precharge is above cut-in, the pump starts while the tank still holds water and then short-cycles. That is one cause of frequent starts. Others: a tank that is too small, a leaking check valve, a dirty switch diaphragm.
Common setting mistakes
- Setting by the scale. Switches are not individually calibrated: a nominal 30/50 PSI switch can really run 28/48 PSI. Trust the gauge.
- Differential too small. The pump starts dozens of times an hour and the motor heats up.
- Cut-out above what the pump can reach. The pump never gets there, the switch never opens, and the motor runs until the thermal protection trips.
- Nuts wound to the end of the thread. The spring is fully compressed and the range is lost.
- No check after the change. After every adjustment run at least one full cycle with a gauge.
When a VFD or soft starter beats a pressure switch
If the switch cycles often or pressure swings between start and stop, the problem is no longer the setting but the way the pump is controlled. A switch is on or off by nature. A variable frequency drive with a pressure sensor holds pressure almost constant and replaces the switch. We described the principle in our piece on a pressure sensor for a pump station.
- Want steady pressure and fewer water hammers: see variable frequency drives and connecting a 4-20 mA pressure sensor.
- Only need a soft start without speed control: soft starters and the soft start guide for pumps.
- Keeping the switch but running the pump from a VFD or generator: VFD setup for use with a pressure switch.
- Worried about dry running or pump sleep: dry-run protection and pump sleep mode.
Bottom line
Set a water pressure switch in the order "differential to maximum, cut-in, cut-out" with a gauge in hand, not by the scale. On an Italtecnica PM/5 or similar it takes 10-15 minutes; on a Condor MDR check first which point the differential screw moves. If the pump still starts too often, look at variable frequency drives or soft starters. Send us the pump model and the motor nameplate and we will tell you whether the switch is enough or the control scheme should change.
