What is Building Maintenance Unit-BMU

What is BMU?

Building Maintenance Unit BMU
Image Source- https://www.coxgomyl.com/

A building maintenance unit or BMU is an automatic or remote-controlled mechanical device, usually suspended from the roof. It moves systematically over some structural surfaces while carrying a suspended platform with human or mechanical robots to clean and maintain the covered surfaces.

The design of BMU is complex. It is permanently fixed on the roof of any building and guided with some structural member to travel overbuilding terrace. It carries any suspended platform-like cradle attached to its end for moving up and down. BMU gives vertical, horizontal, and lateral movement to the suspended platform to access any outer corner or surface of the building.

BMU is well balanced to move on the terrace. Its front boom can be moved up and down using a hydraulic cylinder arrangement. In telescopic BMU, we can get multiple outreaches to access building surfaces. During achieving more outreach, the counterweight can move back to balance the weight. As per the outreach, the counterweight can get automatically get adjusted with the proportional mechanism.

Parts of Building Maintenance Unit

The Building maintenance units are specially designed to clean the exterior surfaces of the HiRISE buildings. So it is necessary to have BMU aesthetically and ergonomically good in a point of view of design, its path of travel, and access location.

Following are the few main construction parts of the BMU.

  1. Base Frame
  2. Vertical Mast
  3. Hydraulic system and cylinders.
  4. Front telescopic boom
  5. Counterweight
  6. Sunpending Arm
  7. Control Panel and Operating Console

Base Frame

The base frame is a rigid structure on which other parts of the BMU mounts. It has a roller at the bottom to rotate on the track with the motor. These rollers carry all weight of the BMU to slide on a track. Bearings are mounted inside the rollers to give better rolling action. It has the arrangement to resist the uplift of certain limits caused during the working of BMU on the field.

The base frame has a top plate welded to the rigid structure to mount the sleeve ring bearing to get desired rotational moment. Sleeve ring bearing selection is very important. The inner ring of the sleeve ring connects to the top plate of the base frame, and its outer ring is connected to the bottom plate of the vertical mast.

Vertical Mast

The mast is a vertical structural member which supports the front telescopic boom and counters weight with other accessories. The outer ring of the sleeve ring bearing is connected to the bottom plate of the mast. With the help of the motors and pinion arrangement, we can rotate the mast at the desired position.  

The top plate of the mast supports the counterweight frame and front boom. These are bolted with the top plate.  

Hydraulic system and Cylinder

The function of the hydraulic cylinder is to lift the telescopic boom at the desired degree to achieve desired cleaning position of the cradle. It uses a hydraulic pump to force hydraulic fluid through pipes connected to the cylinders.

Front Telescopic Boom

The front telescopic boom consists of a boom of the rectangular cross-section, which is hollow from inside. Front telescopic assembly consists of a gradually decreasing rectangular cross-section boom inserted in each other.

During the operation, these booms come outside of each other with the help of motors or hydraulic cylinders. Due to that, we get more outreach to reach each corner of the building façade.


The function of the counterweight is to balance the total weight of the BMU. These are placed on the rear side to balance the weight of the front side and the reaction caused due to the outreach. Its length can adjust as outreach increases of the front telescopic boom.

Suspending arm

Suspending arm is mounted on the end of the telescopic boom for lowering cradle from the terrace of the building.

Control Panel and Operating Console

The Control panel of the machine is an electrical control circuit, protected in weather tight enclosure. Pendent controls of the machine are a detachable operating console that allows the operator to move the BMU easily.

The control system is installed both on the BMU as well as Cradle. However, the control system on the BMU’s is more elaborate. At any one point in time, only one of the control systems can activate.

The controls on the cradle comprise of a cradle rise and lower selector, crossbar slew clockwise and anti-clockwise sector unit, mast slew clockwise and anticlockwise sector unit, trip bar override push button, and emergency stop lockable button.

Regulations while using Building Maintenance MU

As BMU are placed at high heights, there are so many regulations and restrictions are there. Because human safety is prime considerations.

  1. To operate BMU the operator should be trained as per respective norms of the country or certification of the company.
  2. Operator load and suspended load with tools should not exceed its safe working load limit.
  3. Always design BMU with 2.5 of safety factor on its actual suspended load.
  4. It should not be used for wind speed more than 12 m/s.
  5. A proper fall arrest system requires to protect humans from falling.
  6. All tools and tackles are securely placed in the cradle to avoid any tool to fall from the cradle.

Standard for Designing BMU

  • European Norms and British Standard- EN BS 1808:2015 – Safety requirements for suspended access equipment – Design calculations, stability criteria, construction – Examinations and tests.
  • Australian Standard- AS 1418.13—1996 – Cranes (including hoists and winches).
  • A120 STANDARDS COMMITTEE – Safety Requirements for Powered Platforms for Building Maintenance.
  • CSA Z271 – Design of suspended access equipment.

Advantages of the BMU system.

  1. It helps to access the outer surface of the building for cleaning and maintenance.
  2. It is a one-time investment for a cleaning solution.
  3. BMU system is easy to use.

Disadvantages of BMU system.

  1. It is costly.
  2. In bad weather, we cannot use the BMU system.
  3. We can use the BMU system for wind speed below 14m/s. If the wind speed exceeds more than this, we can’t use.

Top Building Maintenance Unit Companies

  1. Cox and Gomyl (Alimak Group)
  2. Manntech (Alimak Group)
  3. Atlas Anchor System Ltd
  4. Tractel
  5. Malt Technics LLC
  6. Global BMU
  7. XSPlatforms
  8. JOMY Inc

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