Description

Mycom Screw Compressor Compound Technical Manual

I’ve seen too many compressor rebuilds go sideways because someone used a volume ratio pulled off a forum. If you’re working on a Mycom Screw Compressor Compound, you need the factory documentation. This Technical Manual from Mayakawa Mfg. runs 72 pages and covers the MCT-05-VB parts list, rotor geometry, and volume ratio selection. It’s the same book I pull off the shelf when a compound compressor comes in for overhaul.

Volume Ratio Selection: L, M, H Explained

The manual breaks down the built-in volume ratio (Vi) into three settings: L = 2.6, M = 3.6, H = 5.8. Those numbers aren’t suggestions. They determine whether the compressor wastes power or runs efficiently. Page 3 of the OCR excerpt shows the formula πi = Pd/Ps and warns that mismatching the ratio to operating conditions is a waste of power. Match the ratio to your refrigerant and load or you’ll be chasing high discharge temperatures.

Compression Cycle: Suction to Discharge

You get the full four-phase breakdown: suction, transfer, compression, discharge. The manual describes how a pair of lobes unmesh on the suction port side, gas flows in, then gets trapped and moved circumferentially at constant suction pressure. When remeshing starts, the trapped volume is reduced and the charge is compressed helically toward the discharge end. No valve mechanism means no vibration or abrasion – but you have to get the clearances right. The manual tells you what to look for.

Rotor Profiles and Lubrication

The male rotor has four convex lobes, the female has six concave lobes. The unsymmetric profile gives high compression efficiency. The manual states wear on the rotors is negligible because they’re well lubricated and the leading edges don’t contact the casing. That’s only true if the oil system is set up per factory spec – and this manual gives you the oil circuit routing. Don’t trust aftermarket diagrams for oil pressure ports.

Parts Breakdown: MCT-05-VB List

Section MCT-05-VB is a dedicated parts list with problem and remedy entries. If a bearing fails or a rotor seizes, you go straight to that list and cross-reference part numbers. Aftermarket catalogs often compress Mycom part numbers into generic categories – that’s how you end up with the wrong thrust bearing. This list uses original Mayakawa numbers.

Why OEM Documentation Matters

Aftermanuals for industrial compressors are notorious for copying specs from older editions. This Technical Manual is a direct scan from Mayakawa Mfg. – no reprints, no third-party edits. The page count, part numbers, and dimension references are what the factory ships with the machine. For background on how screw compressors differ from reciprocating models, refer to the Manual Transmission article or the Air Conditioning Compressor page. But for this specific machine, skip the internet.

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FAQ – Field Questions

Does this manual include wiring diagrams for the control panel?

It covers mechanical parts and operation. Control wiring is not included. You’ll need the separate electrical manual for the panel.

What is the difference between male and female rotor?

The male rotor has four convex lobes driven by the motor; the female has six concave lobes. They rotate at a fixed ratio – 3,000/2,000 rpm at 50 Hz.

How do I find the correct volume ratio for my application?

Page 3 gives the formula Vi^k = πi = Pd/Ps. The manual lists the three ratios (L, M, H) and tells you to choose based on operational conditions. If you don’t have your system pressures, calculate them first. Using the wrong ratio wastes power and drops efficiency.

Can I use this manual for a Mycom single-stage screw compressor?

No. This is for the Screw Compressor Compound only. Single-stage models have different rotor geometry and oil circuits. Buying the wrong manual costs you time and money.

Every time I’ve seen a compound compressor come into the shop with a spec sheet scribbled on a sticky note, it ends up costing a day of teardown to correct clearances. Don’t be that guy. Access the Factory Manual and keep the official specs on your bench. The 72 pages cover the parts list, all four compression phases, and the volume ratio table – exactly what you need to get the job done right the first time.