HML Two-Stage Split Case Pumps
Flow & Pressure Characteristics
Flows To: 900 GPM (204 m³/hr)
Heads To: 950 Feet (290 m)
Temperatures To: 350ºF (177ºC)
Speed Ranges: 3000 RPM To 3600 RPM
1.5×2.5-8 (38/20) – 4×5-11 (100/28)
The HML two-stage split case product line is one of the oldest product lines manufactured by CPS-Pumps. This product line was originally designed in the early 1940’s and continues today to serve the industrial and commercial markets worldwide. The HML was specifically designed to supply water for boiler feed applications. It’s many features and benefits are custom engineered for this market and allow it to be continuously operated for nearly 80 years. Applications in hospitals, schools, universities, manufacturing facilities and other industrial & commercial facilities are only a few of the installations that the HML product line is designed for. With flows through 900 GPM (204 m³/hr) and pressures through 950 Feet (290 m) the HML product line covers a very large hydraulic envelope.
At the heart of the HML product line is the two-stage impeller assembly. This high efficiency, multi-vaned, radial and opposed impeller design allows for a balanced axial thrust keeping the bearing assemblies small and symmetrical. Each of the impeller eyes face the opposite direction balancing the hydraulic thrust of the other. This design feature eliminates the need for any complicated balancing drums simplifying the design and service of the product line. The impellers are investment cast of 304 stainless steel making them extremely smooth and of the highest quality available. This 304 stainless steel material also resists the harsh chemicals used in the boiler feed industry to keep the boiler tubes clean and scale free.
Another industry unique and specifiable feature are the labyrinth style case wear rings. These wear rings have three wear sides and encompass the hub of the impeller eye completely. This allows for two additional pressure breakdown paths, minimizing flow recirculation and keeping the higher pressure fluid in the volute, where it belongs. This design, implemented over 75 years ago, is still industry unique and is the primary reason why our two-stage split cases still have some of the highest efficiencies available in the world today.
Boiler feed fluid temperatures can range from 180ºF to 350ºF and the HML product line stands ready to perform. When we engineered the HML product line years ago, we used larger diameter shafts and larger diameter bearings. It is for this reason that the inboard and outboard bearings (6300 Series) are identical and the need for a duplex outboard bearing is not required, as can be seen on nearly all competitor pumps. This design gives the entire HML product line a minimum L10 bearing life of 50,000 hours, an industry standard. If an engineer or end user insists on a double row bearing at either the inboard or outboard location, we can easily add that bearing upon request. The standard bearing also features “Purge Grease” lubrication. This type of lubrication allows for re-greasing of the bearing housing assembly, with the pump still in operation, and “purges” the old grease out of a port located in the bottom of the bearing housing cap. This allows for all old grease to be easily replaced with new in a very short timeframe and all completed with zero downtime.
For higher temperature applications, the HML also offers a ring-oiled lubrication option. This ring-oiled lubrication is designed for higher temperature applications and features a visible oil reservoir to let your maintenance people know that the pump has proper oil to perform correctly. This design utilizes an oil ring that skims oil from the surface of the oil sump ensuring that only clean oil is used for lubrication. This oil travels up to the shaft, to the bearing and back to the sump. Any contaminants settle to the bottom of the oil sump and will not be drawn back up and into the bearing assembly. A magnetic oil drain plug can also be requested to attract any suspended metallic particles.
Although the HML split case product is nearly 80 years old, it does not mean that enhancements have not been made recently. In the last 10 years, we “unified” the packing housing/seal chambers for two reasons.
1. The new bores allow for no extra line boring or machining when changing from packing to mechanical seal.
2. Newer mechanical seal designs need more room and the unified bores allow for this extra space.
The shaft sleeves are offered in standard bronze and have separate shaft sleeve nuts made of 420 stainless steel. These shaft sleeve nuts are located outside of the fluid assembly keeping them corrosion free and making disassembly of the rotor assembly much easier. Many options are available with regards to packing or mechanical seals allowing for many construction options. An internal Plan 1 flush is standard on the first stage stuffing bow and a drilled external port is located on the second stage box allowing for an easy connection if the application requires it.
The HML two-stage split case has stood the test of time and with thousands of installations world-wide, has a proven track record. For additional information please contact CPS-Pumps. We can help engineer the HML for your next demanding application.