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Compressor : Hitachi


New plastic material coated rotor

This is a new coating that can withstand highly corrosive operating environments!

Are your compressors operating under harsh conditions in which the compressor rotors are being affected by a corrosive environment and by drains that contain compressed air? In environments like this, rotors wear thin due to abnormal corrosion. As a result, the rotor loses its efficiency and in the worst-case scenario, it may become impossible for it to keep running. A new coating has been developed to prevent this phenomenon.
We recommend this new plastic coating to our customers who are dealing with this problem.


The material for this coating is similar to Polytetra fluoro ethylene, but compared to typical Polytetra fluoro ethylene coatings and other coatings, it offers greater consistency and a dramatic reduction in film pin holes.

Moreover, in salt spray corrosion testing, the superiority of this new material was confirmed because the change over time of the material was less than that found in conventional materials.

*Please ask us about extremely corroded coating of rotors.Image: Peeling evaluation graph

Photograph: Example of extreme corrosion
Example of extreme corrosion

Photograph: Rotor coated with the new plastic material
Rotor coated with the new plastic material

Using shaft vibration to monitor status

Most of the problems that occur during compressor operations appear in the form of increased shaft vibration.

  • You can detect abnormal conditions early on by monitoring shaft vibration. It is an effective way to prevent serious breakdowns.
  • Shaft vibration can be continuously detected using non-contact sensors with the overcurrent method, and monitoring results can be displayed digitally on a monitor.
  • Shaft vibration of the main electric motor can also be detected. (Part of the casing needs to be rebuilt)
  • We collect temperature, pressure, and other operating data during cycle inspection services, as well as shaft vibration data to maintain drains.

Photograph: Vibration monitoring equipment

Image: Concept diagram of monitoring shaft vibration

Vibration monitor warning function

  1. Comparative warning (2-stage)
    When measured values exceed setting values
    • Warning lamp (red) lights
    • Relay contact point: On
      → Warning signal outputted to compressor trip circuit
  2. Input over warning
    When an atmosphere signal is input
    • Input lamp (green) goes out
    • (1)Comparative warning signal output prohibited
  3. Warning delay time setting
    • Can be set to divide into in 0.1 sec. increments between 0.1-60.0 sec.

Photograph: Sensor installation location

2-stage intake filter (pre-filter)

Compressors are sometimes installed in environments where there is a great deal of airborne dirt and dust, depending on the products manufactured by our customers. That is why our compressors are designed to eliminate dirt by installing filters on compressor air intakes. In good environments, these filters can operate without maintenance, until auxiliary equipment inspections are performed. However, in dusty environments, the filter quickly becomes clogged, and it is necessary to stop the compressor in order to clean the filter.

That's why we recommend the installation of a pre-filter on the compressor sound-reducing cover to avoid this situation.

Photograph: View of pre-filter
Pre-filter appearance
(for indoor installation)

Advantages of installing a pre-filter

  1. For use in dusty environments
  2. There is no interference with operations because you can easily clean the filter even while the compressor is running.

Pre-filter as installed

This is what the pre-filter looks like when it is installed (right). Insert the packing into the intake in the compressor sound-reducing cover, tighten the bolts, and it is installed. You can see how easy it is.

It's easy to replace the filter, too. Just loosen the mounting bolts, open the top cover, and replace the pre-filter.

Photograph: Pre-filter as installed
Pre-filter as installed

New air filter


We have developed a new air filter for the SDS compressor.

The new air filter can be installed in the existing SDS series. These filters mark a dramatic improvement in terms of maintenance.

We recommend that you try our new air filters when replacing your current filters.

Improved points

To remove or install the filter element, all you have to do is wrap the filter element in place (using a Velcro fastener) because we have changed from the conventional punched-plate, double-layer type to an inner cylinder type.

  • *There is no longer a need to take the trouble of inserting the filter element between the layers of a double-layer punched plate.

Installation in the sound-reducing cover duct

The upper and lower covers no longer need to be removed when installing the filter, which prevents problems.
Along with making the job easier, you can save time because you no longer have to stop the compressor to change the filter.

Image: Improved air filter
Improved air filter

New Y-shaped strainer and drain silencer

The drain outlets of SDS compressors are generally open to the atmosphere (to the drain pit, etc.) via a Y-shaped strainer and drain silencer current models of Y-shaped strainers and drain silencers are made of FC material (gray cast iron) or steel (general-purpose structural steel material). So, even though these parts are treated with a rust-proof coating, they will corrode over years.
We have developed a new Y-shaped strainer and drain silencer using BC material (bronze casting) and SUS (stainless steel) for the orifice, thereby improving corrosion resistance and making these parts smaller and lighter. This makes dismantling and cleaning work easier.

Photograph: Installation location
Installation location

Photograph: Y-shaped strainer and drain silencer
Y-shaped strainer and drain silencer

Installation method

Since these parts are installed with screws, they are easy to set simply by inserting into the Y-shaped strainer mounting flange on the existing base.

Electrostatic precipitator


Oil-free screw compressors discharge oil smoke from the gear reducer to the outside. But given current environmental concerns, there are more and more situations where oily smoke cannot be released into the atmosphere.
By installing an electrostatic precipitator, oily smoke can be returned to the system without discharging it to the atmosphere.


This electrostatic precipitator works by applying a high-voltage electric charge to the oily smoke particles, which are in mist-form. These particles are then separated from the air by adding an electric field. To install, simply remove the existing oily smoke pipe and use the mounting bolts to install the unit onto the flange on the sound-reducing cover. Power is stepped down by a transformer and provided by the oil pump power supply.

Photograph: Electrostatic precipitator
View of Electrostatic precipitator

Improvements in the main motor shaft structure

Shaft sealing

The flange type main motor installed in SDS compressors (with direct connection to the gear case), have a sealed-shaft structure to prevent incursion of lubricating oil in the gear case into the interior of the main motor.

However, over long periods of operation, dust can accumulate in the shaft seal parts and the effectiveness of the shaft seal can deteriorate, causing lubricating oil from the gear case to get into the main electric motor. This can result in a decrease in the insulating resistance of the main motor, oil leakage, and other serious consequences.

Photograph: Main electric motor
View of main electric motor

Advantages to improvements in shaft structure

We can achieve a significant improvement in shaft seal reliability by adding an air line to the interior cover.

  • You can control lubricating oil and help keep it from getting into the main electric motor by increasing the shaft seal performance.
  • This can prevent insulation deterioration due to oil fouling. (Extension of main motor service life)
  • This can prevent oil from spattering (dripping) to the outside.(Prevention of environmental pollution)
  • This is the standard configuration in models starting with the SDS-H Series, and the reliability of this system has been confirmed.

Before improvements

  • The grease viscosity prevents bearing grease from flowing in.
  • Air pressure from the cooling fan prevents lubricating oil from the gear case from getting in.

Image: Before improvements

After improvements

We have achieved an improvement in shaft seal performance by making the changes listed below.

  • Added a labyrinth seal.
  • Added of a shaft seal air line on the inside cover.

Image: After improvements

Notification regarding air coolers


Over long periods of service, air coolers can develop water leaks due to the corrosive properties of coolant water and air.
Some of the problems that can develop in air coolers are:

  1. Pinholes which develop in the tubing
  2. Corrosion of the baffle plates
  3. Water leakage from

the tube expanding

Cooler upgrading

(1)Preventative maintenance

Ways to prevent cooler problems include improving coolant water quality and removing corrosive material from the atmosphere, but these sorts of improvements are virtually impossible to achieve. That's why we recommend that you use the results obtained through overall inspections to develop a plan for preventative maintenance before you have a major breakdown.

(2)Service life and cost comparison

Air cooler service life is significantly influenced by the quality of coolant water. Based on our past experience, a replacement cycle of approximately 7 years can be significantly shortened to 3 years under adverse conditions, depending on water quality. Corrosion-resistant coolers can achieve more than double the service life you can expect with standard coolers. Although the improved coolers can cost 30% more than conventional coolers (in the case of STS-H31 class coolers), they are cheaper in the long run when you consider that you can expect more than double the service life on average.

(3)Differences between standard coolers and coolers with improved corrosion resistance

(3)Differences between standard coolers and coolers with improved corrosion resistance
Items/grade Standard Improved corrosion resistance
Cooler tubing Copper pipe C1020T Cupronickel C7060T
Baffle plate Steel plate SS400 Naval brass C4621P
Tube plate Steel plate SS400 Steel plate SS400
Stay pipe Carbon steel pipe for typical structure STK30 Cupronickel C7060T
Stay bolt Steel rod SS400 Cupronickel C4641BD
Shell Carbon steel tubing SGP Pressure carbon seamless steel pipe

Photograph: Decreased cooling efficiency due to corrosion of air cooler baffle plates