Fault tolerance of pelletizers

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Fault tolerance of pelletizers

Fault tolerance  of pelletizers

Fault tolerance — the property of a technical system to maintain its performance after the failure of one or more components. Fault tolerance is determined by the number of any consecutive single component failures, after which the system as a whole remains functional. The basic level of fault tolerance implies protection against failure of any single element — excluding a single point of failure.

Failure rate — the ratio of the number of failed objects (samples of equipment, products, parts, mechanisms, devices, nodes, etc.) per unit of time to the average number of objects that are working properly in a given period of time, provided that the failed objects are not restored or replaced with serviceable ones. In other words, the failure rate is numerically equal to the number of failures per unit of time attributed to the number of nodes that have worked flawlessly up to this time.

Below are the elements of each granulator and their failure rate according to:

  • «Generic component reliability data for research reactor PSA» INTERNATIONAL ATOMIC ENERGY AGENCY
  • «Aging and Service Wear of Air-Operated Valves Used in Safety-Related Systems at Nuclear Power Plants» Martin Marietta Energy Systems, Inc.
  • «Solenoid Valves used in Safety Instrumented Systems» ASCO Valves
  • «Increased Efficiency of Hydraulic Systems Through Reliability Theory and Monitoring of System Operating Parameters» Jocanović, M. – Šević.

Hydraulic analog (1 piece)

Proportional valve
Pressure compensated relief valves
Gear pump with frequency regulation
Electro-hydraulic valves
Electrical motors
Pressure switch valve
Check valve - flow restrictor
Rubber high-pressure hoses

PU20 module (3 pieces)

Ball valves for gas
Pneumatic actuators rotary
Proportional valves
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Probability of failure at 10,000 hours of operation
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Probability of failure at 10,000 hours of operation

Actuator's resource

High-quality hydraulic / pneumatic cuffs are the basis for proper operation of the hydraulic / pneumatic cylinder. Knowing the characteristics of hydraulic / pneumatic cuffs and what ultimately leads to their failure helps to achieve trouble — free operation of the hydraulic/pneumatic cylinder throughout its service life.


The cuffs play an important role-they hold the liquid/gas and prevent it from leaking between the cylinder components. Cuffs are divided into two main categories: dynamic and static. Dynamic cuffs are used between parts that are in motion relative to each other. The cuffs for the rod sealing system protect the dynamic reciprocating movement of the rod, piston and head. The reciprocating motion of the piston relative to the cylinder is another area of the cylinder that uses dynamic cuffs.

Below is a simple calculation of the resource of the analog drive and the PU20 module:

  • Trelleborg Sealing Solutions PROHIPP 4th Year General Meeting VIC, 26th of May 2008
  • Jack-up cylinders First Selection Offshore Bosch Rexroth
  • ISO 19973 — Pneumatic Fluid Power — Assessment of component reliability by testing

Hydraulic cylinder

  • Resource of cuff seals 500 km;
  • Duration of the pressing cycle: 45 sec;
  • Plunger stroke per cycle: 0,6 meter;

Pneumatic cylinder​

  • Resource of cuff seals: 30 000 км;
  • Duration of the pressing cycle: 12 сек;
  • Plunger stroke per cycle: 0,8 метров;
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Resource of the hydraulic granulator power drive
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Power drive resource of the PU20 module