Model 105

Bellows Type

High-Accuracy Measurement with Built-In Over-Pressure Protection

The Mid-West® Instrument Model 105 Bellows Differential Pressure Gauge provides ±0.5% or ±1.0% full-scale accuracy for low differential pressure applications. Designed with precision and protection in mind, it converts system pressure into a readable signal via a bellows and mechanical linkage.

Key Features:

Bellows Sensing Element: Accurately detects pressure differences.
Two-Piece Body Design: Clamps the sensing and over-pressure assemblies while isolating high- and low-side pressures.
Torque Tube & Range Spring Assembly: Translates bellows movement into gauge pointer rotation or optional electrical signal.
Bi-Directional Over-Pressure Relief Valve: Protects internal components by equalizing pressure in both directions:
- High-Side Over-Pressure: A mechanical stop triggers the relief valve when maximum travel is reached.
- Low-Side Over-Pressure: A spring-loaded valve opens when the pressure exceeds safe limits.

Important Note: This model is highly sensitive—especially at low pressure ranges—and should be protected from sudden pressure spikes or rough handling to maintain accuracy and avoid damage.

model 105 that can feature a square root dial

Product Features/Benefits

Rugged Bellows Sensing Element
Glass Reinforced Thermoplastic Dial case (Panel Mountable)
Weather Resistant & Corrosion Resistant Gauge Front
270° Dial Arc
Shatter Resistant Lens
Over-Range Protection, High over Low and Low over High
5 Year Warranty
For complete model details See bulletin_105_106.pdf
Installation and Operation Manual See Bulletin: im105_106.pdf

Specifications / Configuration

Dial Sizes available: 4-1/2” and 6” Diameters
Dial Scale Ranges: 0-10” H2O to 0-79.9” H2O (0-0.4 PSID to 0-2.9 PSID)
Differential Full Scale Ascending Accuracy available:
±1/2% (ASME B40.1 Grade 2A)
±1% (ASME B40.1 Grade 1A)
Available in a Variety of Dial Scales: Bar, Mbar, kPa, Kg/Cm2, Dual Scale and Square Root for Flow Indication etc.
Working Pressures up to 6000 PSIG (400 Bar)
Operating Temp -40°F to +200°F (-40°C to +93°C)
Weather Protection & Corrosion Resistant
Material of Construction of Body - Aluminum, Carbon Steel, 316/316L Stainless Steel and Brass (Wetted Part)
Internal wetted parts-316 Stainless Steel
Dual Top and Bottom Process connections
O-rings Materials Buna-N, Viton, and Ethylene Propylene
For complete specifications see: Specificationsheet_105-106.pdf

Common Applications

Pressurized Tank Level Monitoring
Stationary Tanks – Horizontal or Vertical
Tanker Transport (For materials such as LOX, CO2, Ammonia, Nitrogen, Helium, Nitrogen, Hydrogen and Argon)
Water Treatment and Air Conditioning Systems
Square Root Dials for Direct Reading of Flow Rates
Pump Performance Monitoring
Hydraulic Filter Monitoring
Filter monitoring for Gases

Additional Options:

Pipe Mounting Kit - 2" U-Bolt
Wall Mounting Kit
Oxygen Cleaning
Maximum Follower Pointer
NACE Certificate (Available for Aluminum and Stainless Steel Bodies only)
CRN – Canadian Registration Number (1500 PSI Safe Working Pressure Stainless Steel Bodies only)

The Mid-West Advantage

5 year warranty
30 + Years Hazardous Location product manufacturer.
OEM and Private Label Capabilities
Fast on-time Deliveries
Friendly Customer Support
Certified Quality System CSA B51-19 SAI GLOBAL

Model 105Documents

Model No.	Differential Pressure Range	Accuracy	Working Pressure	Electrical Available	Electrical IOM
Model 105	0-10" H2O (0-0.4 PSID) to 0-79.9" H2O (0-2.9 PSID)	±1/2% or 1% Note: 1/2% Full Scale available 30" H2O & above	Up to 3,000 PSI	None available
Model 106	0-80" H2O (0-3 PSID) to 0-800" H2O (0-30 PSID)	±1/2 or ±1% FS	Up to 3,000 PSI	MICRO SWITCHES 0-80" H2O to 0-800" H2O, CSA LISTED IND. CONT. EQUIP.
Model 115	0-10" H2O to 0-69.9" H2O Tank Level Applications	±1%	500 PSI (Optional 1,000 PSI)	None available	N/A
Model 116	0-70" H2O to 0-800" H2O Tank Level Applications	±1%	500 PSI (Optional 1,000 PSI)	MICRO SWITCHES 0-80" H2O to 0-800" H2O NEMA 4X, CSA LISTED IND. CONT. EQUIP.