Danfoss KP 35, KP 36 & KPI 38 Pressure Switch Selection Guide
Buy Danfoss products here
A pressure switch is usually noticed only when something stops working.
A pump does not cut off at the right pressure. A compressor trips too late. A boiler or utility line needs pressure protection. A maintenance engineer checks the panel and finds that the old pressure switch has failed, the differential is wrongly selected, or the pressure range does not match the actual process condition.
This is where the Danfoss KP / KPI Series pressure switches become useful for industrial buyers. They are not just on/off switches. They are control and safety devices used to monitor pressure and operate electrical contacts when the pressure reaches a set value.
For Radical TechMart buyers, the key models in this category are:
- Danfoss KP 35
- Danfoss KP 36
- Danfoss KPI 38 / KP 38
The selection should not be done only by model number. The buyer must confirm pressure range, differential, process connection, contact system, media compatibility, enclosure requirement, reset type, and actual application.
What is a Danfoss KP / KPI Pressure Switch?
A Danfoss KP / KPI pressure switch is an electromechanical device that senses pressure and changes an electrical contact when the set pressure point is reached.
In simple words:
- Pressure increases or decreases in the system.
- The pressure acts on the bellows mechanism inside the switch.
- When the pressure reaches the selected cut-in or cut-out point, the electrical contact changes state.
- This contact can be used for pump control, compressor control, alarm, trip, interlock, or panel indication.
The Danfoss data shows KP / KPI pressure switches use an SPDT contact system, which is useful for control-panel wiring because one common input can be wired to either normally open or normally closed logic depending on the application. The PDF also explains that the snap-action contact function helps reduce contact bounce and supports accurate changeover at the cut-out point.
Why Correct Pressure Switch Selection Matters
In actual plant conditions, wrong pressure switch selection can create repeated downtime.
A low-range switch used in a higher-pressure system may fail early or become unsafe. A high-range switch used in a low-pressure application may not give accurate switching control. A wrong differential can cause short cycling in pumps or compressors. A wrong enclosure can create problems in dusty or wet installations.
For example, if a pump system needs automatic start-stop control, the differential is very important. If the differential is too narrow, the pump may cycle frequently. If it is too wide, pressure may drop more than acceptable before restart.
This is why the buyer should not ask only, “What is the price of Danfoss KP 35?” A better question is:
“Is Danfoss KP 35 suitable for my pressure range, media, switch logic, enclosure condition, and control panel wiring?”
How Danfoss KP / KPI Pressure Switches Work
The pressure switch works through a mechanical pressure-sensing system and electrical switching mechanism.
When process pressure enters the pressure connection, it acts on the bellows. The bellows movement is transferred to a spring and contact mechanism. Once the set pressure is reached, the contact changes over quickly through a snap-action function.
This matters because industrial systems often have vibration, pressure pulsation, motor starting current, and repeated switching cycles. A stable snap-action contact helps the switch operate more reliably than a slow or weak contact movement.
The Danfoss PDF also defines key terms clearly:
- Range setting / set point: pressure range where contact changeover happens.
- Differential: difference between contact changeover on rising and falling pressure.
- Automatic reset: unit restarts automatically after stop.
- Manual reset: unit requires external reset action before operation resumes.
- Permissible operating pressure: highest pressure the unit can be continuously exposed to.
Types of Danfoss KP / KPI Series Products Available
Danfoss KP 35
Danfoss KP 35 is suitable when the application needs low-pressure to medium-pressure control. It is commonly selected for systems where pressure monitoring, pump control, compressor protection, or general industrial pressure switching is required.
Technical points to note:
- Product type: Pressure switch
- Model: Danfoss KP 35
- Setting range: -0.2 to 7.5 bar
- Differential: 0.7 to 4.0 bar
- Permissible operating pressure: 17 bar
- Max. test pressure: 22 bar
- Pressure connection: G 1/4 A
- Contact material options: silver / gold-plated depending on variant
- Variants include IP55 transparent enclosure and stainless steel version options in the PDF listing.
Where it is commonly used:
- Pump control panels
- Compressor control circuits
- HVAC pressure monitoring
- Utility pressure control
- Process equipment pressure interlock
- General industrial automation panels
Danfoss KP 36
Danfoss KP 36 is suitable when the pressure requirement is higher than KP 35. It is often selected for medium-pressure applications where the switch must operate in a stronger pressure range.
Technical points to note:
- Product type: Pressure switch
- Model: Danfoss KP 36
- Setting range: 2.0 to 14.0 bar for common listed variants
- Differential: 0.7 to 4.0 bar
- Additional listed range option: 4.0 to 12.0 bar with 0.5 to 1.6 bar differential
- Permissible operating pressure: 17 bar
- Max. test pressure: 22 bar
- Pressure connection: G 1/4 A
- Contact material options: silver / gold depending on variant
- IP55 transparent enclosure and stainless steel version options are shown for selected variants.
Where it is commonly used:
- Compressor pressure control
- Pump discharge pressure monitoring
- HVAC and refrigeration utility lines
- Industrial skid control panels
- Hydraulic or pneumatic support systems where compatible
- Alarm and trip logic in machine panels
Danfoss KPI 38
In your store category, KPI 38 can be positioned as the high-pressure option in this KP / KPI product group. It is suitable when the application needs higher pressure switching than KP 35 or KP 36.
Technical points to note:
- Product type: Pressure switch
- Model: Danfoss KPI 38
- Setting range: 8.0 to 28.0 bar
- Differential: 1.8 to 6.0 bar
- Permissible operating pressure: 30 bar
- Max. test pressure: 30 bar
- Pressure connection: G 1/4 A
- Contact material: silver in listed variants
- Listed code numbers include 060-508166 and 060-541866 depending on variant.
Where it is commonly used:
- High-pressure compressor applications
- Pump discharge pressure protection
- Industrial pressure alarm systems
- Process utility pressure monitoring
- Machine safety interlock circuits
- HVAC and refrigeration pressure control where compatible
Quick Comparison: KP 35 vs KP 36 vs KPI 38
| Model | Practical Selection Zone | Setting Range | Differential | Best Use Case |
|---|---|---|---|---|
| Danfoss KP 35 | Low to medium pressure | -0.2 to 7.5 bar | 0.7 to 4.0 bar | Pump, compressor, HVAC and general pressure control |
| Danfoss KP 36 | Medium pressure | 2.0 to 14.0 bar | 0.7 to 4.0 bar | Higher pump/compressor pressure switching than KP 35 |
| Danfoss KPI 38 | Higher pressure | 8.0 to 28.0 bar | 1.8 to 6.0 bar | High-pressure cut-out, alarm, protection and control |
Key Selection Factors
1. Pressure Range
First confirm the actual working pressure and required switching pressure.
Do not select the switch at the extreme end of its range if avoidable. A better selection keeps the normal switching point comfortably inside the working range.
2. Differential
Differential controls the gap between cut-in and cut-out.
This matters in pump and compressor applications. Too small a differential may cause frequent cycling. Too large a differential may allow pressure to drop or rise more than the process can tolerate.
3. Reset Type
Automatic reset is useful for normal control. Manual reset is better for safety or fault conditions where the operator must check the system before restarting.
4. Contact Rating
Check the contact rating before connecting the switch directly to a motor starter, relay, contactor, PLC input, alarm circuit, or panel indication. The Danfoss PDF lists SPDT contact systems and contact load data for KP / KPI models.
5. Enclosure Requirement
The PDF mentions IP30 / IP44 / IP55 enclosure possibilities depending on mounting and enclosure arrangement. IP55 requires mounting in a suitable IP55 enclosure.
6. Media Compatibility
Confirm whether the pressure switch is suitable for the actual media: air, water, refrigerant, gas, steam, oil, or other fluid. Do not assume one model suits every media.
7. Process Connection
Confirm G 1/4 A or the required connection thread before ordering. Wrong pressure connection can delay installation and may require unsafe site modification.
Common Applications
Danfoss KP / KPI pressure switches are commonly used in:
- Pump control systems
- Compressor panels
- HVAC systems
- Refrigeration support systems
- Industrial utility lines
- Boiler and pressure monitoring systems
- OEM machines
- Process automation panels
- Alarm and interlock circuits
- Maintenance replacement applications
Common Mistakes to Avoid
| Mistake | Why It Creates Problems |
|---|---|
| Selecting only by model number | Same-looking switches may have different ranges and reset types |
| Ignoring differential | Can cause pump/compressor short cycling |
| Not checking pressure connection | Installation may not match existing piping |
| Using KP 35 where KP 36 or KPI 38 is needed | The switch may operate outside the correct range |
| Ignoring enclosure/IP requirement | Dust, moisture or outdoor exposure can reduce service life |
| Not confirming contact rating | Electrical load may exceed switch capability |
| Ignoring media compatibility | Internal parts may not suit the actual fluid |
| Replacing old switch without checking datasheet | Old installation may already have been wrongly selected |
Do This, Not That
| Do This | Not This |
|---|---|
| Select by pressure range and differential | Select only by lowest price |
| Confirm reset type | Assume every model is automatic reset |
| Check process connection | Force-fit at site |
| Match contact rating with panel wiring | Directly connect unknown load |
| Confirm IP/enclosure requirement | Use standard enclosure in wet/dusty area |
| Verify media compatibility | Use one model for every application |
Quick Selection Checklist
- Confirm actual working pressure.
- Confirm required cut-in and cut-out pressure.
- Select KP 35, KP 36, or KPI 38 based on pressure range.
- Check differential requirement.
- Confirm automatic or manual reset.
- Confirm pressure connection.
- Check media compatibility.
- Check contact rating and wiring logic.
- Confirm enclosure/IP requirement.
- Verify datasheet, code number, and availability before purchase.
Why Buy Danfoss KP / KPI Pressure Switches from Radical TechMart?
At Radical TechMart, the focus is not only to supply the product, but to help customers select the right pressure switch for the right application.
This matters because a pressure switch is often part of a larger control system. It may connect to a relay, contactor, PLC input, alarm circuit, compressor panel, pump panel, or machine interlock. A wrong selection can create repeated trips, wrong switching, maintenance difficulty, and downtime.
Radical TechMart can support buyers with:
- Danfoss KP / KPI pressure switch selection
- Model comparison between KP 35, KP 36 and KPI 38
- Datasheet and specification checking
- Pricing and availability support
- Replacement selection guidance
- Industrial pressure control product inquiry support
Final Thoughts
The right Danfoss KP / KPI pressure switch is not selected only by price or model number. It is selected by understanding the pressure range, differential, reset logic, contact rating, process connection, enclosure requirement, and actual field application.
For low to medium pressure applications, Danfoss KP 35 may be suitable. For medium-pressure applications, Danfoss KP 36 becomes a stronger option. For higher-pressure switching, Danfoss KPI 38 should be checked.
In industrial applications, the right instrument is not selected only by price or model number. It is selected by understanding the process, the signal, the environment, and the final control requirement.
FAQs
1. What is the difference between Danfoss KP 35 and KP 36?
Danfoss KP 35 is generally used for lower pressure range applications, while KP 36 is selected for higher pressure requirements. KP 35 is listed with a -0.2 to 7.5 bar setting range, while KP 36 is listed with common variants around 2.0 to 14.0 bar.
2. What is Danfoss KPI 38 used for?
Danfoss KPI 38 / KP 38 is suitable for higher-pressure switching applications. It is commonly selected for compressor, pump, high-pressure alarm, cut-out, and control-panel interlock applications.
3. Can Danfoss KP / KPI pressure switches connect to PLC panels?
Yes, they can be wired into PLC, relay, alarm, or control-panel circuits using their electrical contact output. However, contact rating, wiring logic, and electrical load must be confirmed before installation.
4. What does differential mean in a pressure switch?
Differential is the difference between the pressure point where the switch changes state and the pressure point where it resets. It is important for stable pump and compressor operation.
5. Which is better: automatic reset or manual reset?
Automatic reset is suitable for normal control applications. Manual reset is better for safety or fault conditions where the operator must inspect the system before restarting.
6. Is KP 35 suitable for high-pressure applications?
No, KP 35 should not be selected for high-pressure applications beyond its suitable range. For higher pressure, KP 36 or KPI 38 should be checked depending on the actual pressure requirement.
7. What should I confirm before buying a Danfoss KP / KPI pressure switch?
Confirm pressure range, differential, reset type, pressure connection, media compatibility, contact rating, enclosure/IP requirement, code number, and datasheet before purchase.
