Residual Pressure in Auxiliary Hydraulics on the 1989 Case 1845C Skid Steer

[MikePhua]

The 1845C and Case’s Skid Steer Legacy
The Case 1845C skid steer loader, introduced in the mid-1980s and produced into the early 2000s, became one of the most iconic machines in compact construction. With a rated operating capacity of around 1,700 lbs and a 51 hp diesel engine, the 1845C was known for its mechanical simplicity, robust frame, and reliable chain drive system. Case Corporation, founded in 1842, had already established dominance in agricultural and construction equipment, and the 1845C cemented its reputation in the compact loader segment.
The auxiliary hydraulic system on the 1845C allows operators to run attachments such as augers, trenchers, and grapples. These hydraulics are powered by a gear pump and controlled via a manual valve system. While effective, the system can exhibit residual pressure in the auxiliary lines after shutdown, leading to difficulty in connecting or disconnecting attachments.
Understanding Residual Pressure in Hydraulic Circuits
Residual pressure refers to the hydraulic pressure that remains trapped in a line or circuit after the machine is turned off. In the 1845C, this typically occurs in the auxiliary lines due to:

• Lack of pressure relief after engine shutdown
  
• Heat expansion of hydraulic fluid in closed lines
  
• Check valves preventing backflow
  
• Manual valve position at shutdown retaining pressure
  

Symptoms include:

• Difficulty connecting quick couplers
  
• Hydraulic oil spurting during disconnection
  
• Attachments refusing to engage or disengage
  
• Audible hiss or pop when lines are opened
  

In Alberta, a contractor struggled to connect a trencher to his 1845C. After letting the machine sit in the sun, the residual pressure built up in the auxiliary lines. He released the pressure manually by loosening the coupler slightly and cycling the valve with the engine off.
Design Limitations and Manual Relief Strategies
Unlike modern skid steers with automatic pressure relief valves or electronic solenoids, the 1845C relies on manual control. The auxiliary valve is cable-actuated and does not automatically vent pressure when the engine shuts down.
To relieve pressure manually:

• Shut off the engine
  
• Move the auxiliary control lever back and forth several times
  
• Loosen the coupler slightly to bleed residual pressure
  
• Use a rag to catch any escaping fluid
  
• Avoid disconnecting under load or high temperature
  

In Michigan, a fleet manager added a manual ball valve to the auxiliary return line. This allowed technicians to vent pressure safely before swapping attachments, reducing downtime and improving safety.
Hydraulic Fluid Expansion and Thermal Effects
Hydraulic fluid expands with heat. If the machine is parked after heavy use or in direct sunlight, the fluid in the auxiliary lines can pressurize even without pump input. This thermal expansion is a common cause of residual pressure in older machines.
Preventive measures:

• Park in shade when possible
  
• Allow machine to cool before disconnecting attachments
  
• Use quick couplers rated for high residual pressure
  
• Install thermal relief valves if operating in hot climates
  

In Finland, a forestry crew installed a thermal relief valve on their 1845C’s auxiliary circuit. The valve opened at 250 psi, venting excess pressure into the return line and preventing coupler damage.
Upgrades and Retrofit Options
To modernize the 1845C’s hydraulic system:

• Install a pressure relief block with manual override
  
• Upgrade to flat-face couplers with built-in pressure release
  
• Add a pilot-operated check valve with external venting
  
• Replace worn hoses and couplers to reduce sealing resistance
  

Recommended specs:

• Relief valve setting: 2,500 psi
  
• Coupler type: ISO 16028 flat-face
  
• Hose rating: SAE 100R2 minimum
  
• Valve block: 3,000 psi rated with manual dump port
  

In Texas, a contractor retrofitted his 1845C with a hydraulic manifold that included a pressure release button. This allowed operators to depressurize the system before changing attachments, reducing fluid loss and improving workflow.
Operator Training and Safety Protocols
Operators should be trained to:

• Recognize signs of residual pressure
  
• Avoid forcing couplers under pressure
  
• Use gloves and eye protection during disconnection
  
• Report stiff or leaking couplers for inspection
  
• Cycle controls after shutdown to vent trapped pressure
  

A contractor in Shanghai added a laminated instruction card to the cab of each 1845C unit. The card outlined shutdown procedures and pressure relief steps, reducing hydraulic incidents by 70% over six months.
Conclusion
Residual pressure in the auxiliary hydraulics of the Case 1845C is a manageable issue rooted in the machine’s mechanical design and thermal behavior. With proper technique, minor upgrades, and operator awareness, pressure-related problems can be minimized. In compact loaders, control isn’t just about movement—it’s about managing what stays behind when the engine stops.