Introduction
The document introduces the MK XIIA Oscillamatic® Controller by Williams Instrument Incorporated, highlighting its features, design improvements, and recommended applications.

Specifications
- Wide supply pressure range: 30 – 100 psig.
- Accuracy and repeatability: ± 1.75% at 30 PSI to ± 2% at 45 SPM with clean, dry instrument air.
- Versatility: Standard speed range of 1-45 SPM with a 10:1 turndown in one setting.
- Low maintenance: Minimal internal moving parts, easy assembly and disassembly.

Design Improvements
- Constructed with 316SS Stainless Steel for maximum corrosion resistance.
- Diaphragm-style design for minimal maintenance.
- No oil or grease required.
- Hardened 17-4 ph Stainless Steel seats.
- New bolt design for easy diaphragm access.
- Bottom plug for servicing pilot plug and lower spring.
- Optional 3-15 CSM port hole.

Recommended Applications
- Suitable for corrosive environments and gases, both onshore and offshore.
- Compatible with V and W Series Pneumatic Plunger Pumps and LD and HD Series Pneumatic Diaphragm Pumps.
- Can retrofit older style pump controllers.

Controller Comparison
- MK XIIA: 30-100 PSI, 316 ss, 1-45 SPM, Neoprene, Buna N, Viton® Diaphragm.
- MK X: 35-100 PSI, 316 ss, 1-45 SPM, Buna/TFE, Viton®/TFE U-Cup.
- MK VII: 50-90 PSI, Anodized Aluminum, 1-45 SPM, Neoprene, Viton® Diaphragm.
- MK II: 25-65 PSI, Anodized Aluminum, 1-45 SPM, Neoprene, Viton® Diaphragm.

Physical/Functional Description
The MK XIIA operates similarly to the MK X Controller, using flexible diaphragms instead of sliding seals. It features a capillary tube controlled by a needle valve to transfer supply air/gas between chambers. The spool's position controls the air/gas supply and exhaust to the pump.

General Operating Sequence
The spool spring moves the spool to its highest position, unseating the pilot plug and allowing air/gas to enter the pump. As pressure builds, the spool moves down, seating the pilot plug and shutting off the supply. The process repeats as pressure decreases.

Disassembly and Reassembly Procedures
Disassembly:
1. Remove the red cap and socket head cap screws.
2. Separate the upper valve body and remove the inner diaphragm assembly.
3. Remove the spool spring, bottom plug, lower spring, and pilot plug.
4. Disassemble the inner diaphragm and spool assembly.

Reassembly:
1. Reassemble the diaphragms and inner spacer.
2. Install the mid ring and outer sleeve.
3. Insert the inner assembly into the lower controller body.
4. Align capillary holes and secure with body screws.

Contact Information
Williams Instrument Incorporated, 201 Ivyland Road, Ivyland, PA 18974 USA. Phone: (800) 235-3421, (215) 293-0415. Fax: (215) 293-0498. Email: [email protected].