Installation Guide
Manual Lever Pressure Switch
MPSM1 / MPSHDM1
Manual shutoff at the switch.
Which Switch Do You Have?
MPS | Standard
Confirm the part number printed on your switch cover.
MPSHD | Heavy Duty
Same lever function. Heavy-duty electrical design.
Before You Start
Verify model, voltage/HP ratings, pressure range, a clear sensing connection and correct tank air charge. Check the switch label and its enclosed wiring diagram.
Installation | 4 Simple Steps
Disconnect Power. Relieve Pressure.
A qualified installer locks out the correct breaker, verifies zero voltage, then opens a drain until the gauge reads 0 PSI.
Check the Tank and Pressure Connection.
Check precharge with the water side drained. Remove sediment from the pressure sensing port; replace damaged or restricted fittings.
Install the Pressure Switch.
Use suitable thread sealant on compatible male pipe threads. Keep the pressure opening clear and avoid twisting or damaging the switch housing.
Connect Wiring. Replace the Cover.
A qualified installer follows the markings and model wiring instructions, verifies grounding and ratings, then secures the cover before restoring power.
Operation + Safe Startup
MPSM1 / MPSHDM1 | Follow the lever markings on your exact model.
How the Lever Works
M1 | Manual Cut-Out Lever
With the lever ON, the switch starts and stops the pump at the selected pressure settings. Move the lever to OFF to hold the pump off. Return it to ON when normal service should resume.
OFF is a switch control position, NOT an electrical disconnect. NEVER service the equipment using the lever alone.
When to Use the Lever
Use the manual OFF position for an intentional pump shutdown under appropriate supervision. Do not use this lever for low-pressure dry-run protection. The M1 is not an M4 low-pressure-cutoff switch.
Startup Check | Qualified Installer
1. Restore
Confirm cover is secured. Restore power under qualified supervision.
2. Observe
Using a working gauge, verify pump starts and stops at correct pressures.
3. Stop If
Stop for unsafe pressure, repeat trips or abnormal cycling.
Bladder Tank Precharge — Water Side Empty
| Pressure Setting | Precharge |
|---|---|
| 20/40 PSI | 18 PSI |
| 30/50 PSI | 28 PSI |
| 40/60 PSI | 38 PSI |
Important Safety + Legal Notice
BEFORE ANY WORK: Disconnect and lock out power, verify zero voltage with a properly rated tester, and relieve system pressure. The manual OFF lever is NOT an electrical disconnect. Never rely on it to make wiring safe.
QUALIFIED INSTALLATION: Only a qualified electrician or trained pump technician should install, wire, adjust or service this switch. Follow the model wiring diagram, nameplate ratings, NEC and local codes. Ground correctly and secure the cover before restoring power.
PRODUCT LIMITATIONS: The M1 lever provides manual pump shutoff only; it is NOT low-water, low-pressure or dry-run protection. Never bypass safety devices or alter the switch. Improper wiring, installation or use may cause shock, fire, injury, death or property damage.
RESPONSIBILITY: Installers and users must follow these instructions and applicable codes. To the extent permitted by law, Merrill disclaims responsibility for losses caused by misuse, unauthorized changes or installation contrary to these instructions. This notice does not exclude liability that law prohibits limiting.