Siemens QPL25.050B Gas Pressure Switch

Siemens QPL25.050B is a high-performance gas pressure switch. Designed for medium and low pressure monitoring ranging from 5-50 mbar, it features IP54 protection grade and a mechanical service life of 100,000 cycles. It is widely used for safety protection of combustion systems. Check model parameters, pressure range and mounting interface during procurement to ensure full compatibility with system requirements.

Model Code Definition

Code Segment	Meaning	Description
QPL	Product series code	Basic series of Siemens gas pressure switches for gas and air pressure monitoring
25	Structure & rated parameters	Series 25, rated current 6A AC, rated voltage 250V AC/DC, IP54 protection
50	Pressure adjustment range	Adjustable range: 5-50 mbar (0.5-5.0 kPa)
B	Version mark	Standard type, automatic reset, SPDT contact configuration

Core Specification Parameters

Category	Specifications	Remarks
Basic Parameters
Product Type	Mechanical gas pressure switch	Safety monitoring for combustion systems
Order No.	1117087	Official Siemens part number
Adjustment Range	5-50 mbar (0.5-5.0 kPa)	Adjustable set point
Max Working Pressure	690 mbar (69 kPa)	Upper limit of continuous operating pressure
Switch Differential	Approx. 5-10 mbar	Pressure difference between switch-on and switch-off
Electrical Parameters
Rated Voltage	AC 250V / DC 250V	Maximum operating voltage
Rated Current	AC 6A / DC 1A	Resistive load
Contact Type	SPDT	1 normally open + 1 normally closed
Electrical Connection	Terminal box compliant with DIN EN 175 301-803	Class 3 insulation protection
Mechanical & Environmental Parameters
Pressure Port	G1/4 internal thread (ISO228)	Center position at bottom casing
Measuring Port	Ø9mm, 10mm length with locking screw	For pressure calibration
Ambient Temperature	-20°C ~ +60°C	Operating temperature range
Medium Temperature	-40°C ~ +60°C	Applicable gas temperature
Protection Grade	IP54	Dustproof and waterproof
Mechanical Lifespan	100,000 cycles	Switch actuation times
Applicable Media	Class 1/2/3 gases & non-corrosive gas	Natural gas, liquefied petroleum gas, etc.

Full QPL25 Series Model List

Model	Pressure Range	Max Working Pressure	Remarks
QPL25.003B	0.3-3 mbar	690 mbar	Low pressure monitoring
QPL25.010B	1-10 mbar	690 mbar	Ultra-low pressure application
QPL25.050B	5-50 mbar	690 mbar	Standard medium-low pressure
QPL25.150B	15-150 mbar	690 mbar	Medium pressure monitoring
QPL25.500B	100-500 mbar	720 mbar	High pressure monitoring

Cross-brand Replacement Comparison

Brand	Model	Pressure Range	Main Differences	Replacement Suggestion
Siemens	QPL25.050B	5-50 mbar	Original authentic product, high stability	Priority choice
Honeywell	C6097A	5-50 mbar	Lower price, similar response speed	Direct replacement
Danfoss	KPI 36	5-50 mbar	Different mechanical structure, high adjustment precision	Verify mounting dimensions
Dungs	LGW50A2	5-50 mbar	German brand, reliable quality	Fully compatible
Baltur	PAMPA	5-50 mbar	Burner dedicated, cost-effective	Suitable for Baltur combustion systems

Common Troubleshooting & Maintenance

5.1 Common Faults & Causes

Fault Phenomenon	Possible Causes	Troubleshooting Steps
No switch action under normal pressure	Improper setpoint; oxidized/damaged contacts; aging/damaged diaphragm; loose wiring	Recalibrate setpoint; test contact continuity; inspect diaphragm; fasten terminals
No switching under abnormal pressure	Excessive switch differential; mechanical stuck; spring fatigue	Adjust differential; clean moving parts; replace spring assembly
Frequent contact ablation	Overload; unstable voltage; mismatched contact material	Check load current; install surge suppressor; replace contact assembly
Inaccurate pressure reading	Blocked measuring port; deformed diaphragm; calibration error	Clean port; replace diaphragm; recalibrate with standard pressure source

5.2 Maintenance Guidelines

Safety Precaution

Cut off gas supply and release pressure

Disconnect power supply

Cool down equipment to room temperature

Calibration Procedure

① Remove protective cover and locate adjusting screw

② Connect standard pressure source and set target value

③ Clockwise rotation increases set pressure, counter-clockwise decreases

④ Test switching action and confirm accurate trigger point

⑤ Reinstall cover and ensure tight sealing

Component Replacement

Diaphragm: Dismount with special tools, pay attention to gasket installation direction

Contact: Replace whole switch module instead of single contact

Spring: Use identical specification spare part to guarantee precision

Application Environment & Industry Cases

6.1 Applicable Scenarios

✅ Recommended Applications

Safety monitoring for industrial & civil gas burners

Pressure protection system of gas boilers

Pressure control of natural gas pipelines

Gas supply system of industrial furnaces

Pressure monitoring for biogas power generation equipment

❌ Inadmissible Applications

High-pressure gas system over 690 mbar

Corrosive gas atmosphere

Medium temperature exceeding 60°C or below -20°C

Severe vibration and outdoor exposed installation without protection

6.2 Typical Industry Applications

Industry	Application	Function
HVAC	Commercial gas boiler	Monitor gas pressure to ensure combustion efficiency and safety
Food Processing	Baking furnace gas system	Avoid incomplete combustion caused by low pressure
Energy Industry	Biogas power station	Stabilize biogas pressure and protect generating units
Manufacturing	Ceramic kiln	Precise temperature control via gas pressure regulation
Commercial Kitchen	Large cooking equipment	Safety interlock to prevent gas leakage accidents

Selection Tips & Avoidable Risks

Selection Mnemonic

QPL series for gas service, 25 stands for 6A rating

Last three digits define pressure range, B means standard auto-reset

050 model fits 5-50 mbar, G1/4 thread for installation

IP54 solid protection, match gas medium properly

Key Notes

Pressure Matching

Keep actual working pressure within 20%-80% of adjustment range to maintain accuracy.

Installation Requirements

Mount vertically with diaphragm downward to avoid condensed water accumulation.

Install filter at pressure port to prevent internal impurity damage.

Secure wiring firmly to avoid false triggering.

Safety Regulations

Interlock with gas leakage alarm device.

Conduct regular inspection and calibration every 6 months.

Perform pressure and leakage test after maintenance.

Purchase Notice

Choose genuine Siemens products; counterfeit items have unstable quality.

Keep original package and certificate for after-sales service.

Working Principle of QPL25.050B

Core principle: Air pressure deforms diaphragm, mechanical linkage drives contact on-off to realize overpressure interlock protection

Pressure Sensing

Gas flows into inner chamber through G1/4 port and acts on rubber diaphragm, driving axial displacement with pressure variation.

Mechanical Force Balance

Diaphragm thrust counterbalances preset spring tension. Rotate adjusting screw to change spring preload and set trigger pressure threshold.

Linkage Actuation

When pressure rises to set value, diaphragm overcomes spring resistance and pushes rod to drive lever mechanism. Spring rebounds when pressure drops below threshold.

Contact Switching

Lever movement switches SPDT contacts, reverses circuit status and transmits electric signal for burner start-stop and alarm interlock.

Differential Pressure Stabilization

Fixed pressure differential prevents frequent switching and unnecessary equipment startup/shutdown.

Reset Mode

Standard automatic reset; contacts recover initial state once pressure returns to normal range.

Application Scenarios of QPL25.050B

Applicable Sites

Low pressure monitoring and protection for gas boilers and water heaters
Supply pressure interlock control of oil and gas industrial burners
Pressure stabilization detection for commercial kitchen stoves and hot air furnaces
Medium-low pressure monitoring of natural gas and liquefied gas pipelines
Safety protection for furnace and drying equipment gas supply
Start-stop interlock for clean combustible gas such as biogas and coal gas

Forbidden Sites