The Cressi MC9 1st Stage is a component of a diving regulator system, designed for service, repair, and operative maintenance. This manual provides detailed procedures for disassembling, assembling, and setting the MC9 1st Stage, including both INT and DIN models.
Function Description:
The MC9 1st Stage is a crucial part of a scuba diving regulator, responsible for reducing the high pressure from a scuba tank to an intermediate pressure that can be further reduced by a second stage regulator for breathing. It is an overbalanced diaphragm-type first stage, meaning the intermediate pressure increases slightly as the tank pressure drops, which helps maintain consistent performance at varying tank pressures. The manual covers the maintenance and repair of this device, ensuring its safe and proper operation.
Important Technical Specifications:
- Intermediate Pressure Setting: The MC9 1st Stage is designed to be set at an intermediate pressure of 10 bars (146 psi).
- Pressure Compensation: The regulator is overbalanced, leading to a slight increase in intermediate pressure as tank pressure decreases (approximately +0.6 bar / +9 psi at 50 bar / 725 psi tank pressure).
- Oxygen Compatibility: According to European Standard, the procedures described are pertinent for equipment meant for use with air (21% oxygen, 79% nitrogen - EEC Countries Only).
- Torque Specifications:
- Yoke nut blocking (INT model): 30 Nm / 266 in-lbs.
- DIN filter body tightening (DIN model): 30 Nm / 266 in-lbs.
- DIN connector tightening (DIN model): 10 Nm / 88.5 in-lbs.
- Tools Required:
- HZ 709004: Extraction point tool
- HZ 709016: Tool to remove the orifice
- HZ 709008: Threaded bar to tighten the regulator in the vice
- HZ 709012: Yoke nut socket and wrench
- HZ 709018: Removing yoke tool
- HZ 709006: Allen key 6 mm
- Dynamometric wrench (unavailable in the provided image, but specified for torque settings)
- HZ 710010: 1st stage setting pressure gauge
- Plastic hammer (for removing oxidation traces)
- Large adjustable spanner (alternative for yoke nut removal if special spanner is unavailable)
- 24 mm hexagonal spanner (for unscrewing DIN filter)
- 30 mm hexagonal spanner (for removing closing disk)
Usage Features:
The MC9 1st Stage is designed for use in scuba diving. The manual emphasizes that maintenance and repair operations should only be performed by trained personnel at Authorized Cressi-Sub Centers. Users are explicitly warned against performing maintenance themselves. The regulator is designed to be connected to a pressurized tank (200 bars / 2900 psi) for setting and testing.
Maintenance Features:
- Annual Replacement Kit (HZ 800047): Cressi-Sub recommends complete regulator maintenance at least once a year, or more frequently with intensive use. This maintenance must include the replacement of all components provided in the annual equipment maintenance kit. The kit includes:
- HZ 800055: 1 External Hydrostatic Diaphragm (MC9 S.C. Only)
- HZ 800011: 1 Diaphragm
- HZ 800062: 1 Back-Up Ring
- HZ 800057: 1 Sintered Filter
- HZ 800085: 1 HP Valve
- HZ 800059: 1 HP Valve Jacket
- HZ 800082: 1 Pin Support
- O-Rings: HZ 800066, HZ 730132, HZ 800043, HZ 730108, HZ 800057, HZ 800062
- Cleaning:
- Metal parts should be washed with hot water and neutral detergent, then rinsed with fresh water.
- Concretions should be removed using ultrasound cleaning or diluted acid solutions, followed by thorough rinsing.
- Acids or solvents should not be used on rubber components.
- Lubrication:
- New O-rings must be greased with a thin layer of lubricant to minimize damage during assembly.
- Metal threading can be lubricated with grease on the first two rings of threading.
- Thorough lubrication of the O-Ring into the balancing chamber is crucial for the HP valve to function perfectly.
- O-Ring Replacement: O-rings should be removed and replaced using a plastic tool or a round-pointed metal tool to avoid damaging the O-ring seat. Pressing the sides of the O-ring to create a bulge facilitates insertion of the tool. Only original Cressi-Sub spare parts should be used.
- Oxidation Removal: If the regulator has been used underwater for extended periods and shows oxidation, gently tapping the perimeter of the first stage closing disk with a plastic hammer can be useful.
- Disassembly Warnings: Avoid using wrench extensions during disassembly if operations are difficult, as this may damage the equipment. Contact Cressi-Sub in such cases.
- Assembly Procedures: Detailed steps are provided for assembling the various components, including the orifice, HP valve, filter, pin pusher, diaphragm, spring washer, and setting screw. Specific torque values are given for critical connections.
- Setting Procedures:
- Connect a setting pressure gauge to an LP port.
- Connect the regulator (with both 1st and 2nd stages) to a 200 bar (2900 psi) pressurized tank or workbench.
- Slowly open the air valve while pressing the second stage air outlet button multiple times.
- Adjust the intermediate pressure to 10 bars (146 psi) using a 6 mm Allen wrench on the setting screw (clockwise to increase, anticlockwise to decrease).
- Ensure the regulator is discharged before adjusting the intermediate pressure to avoid incorrect readings.
- Verify that the intermediate pressure is stable and does not increase after pressing the second stage discharge button multiple times.
- After setting, the first stage pressure should decrease by less than 1 bar (14.6 psi) when the second stage discharge button is pressed.
- Record Keeping: A "Maintenance/Service Record" is provided to document details such as model, serial number, date, dealer name, technician name, notes on procedures (including scheduled maintenance), and signature. This record also includes checkboxes for various maintenance tasks and replacement parts.
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