title: Selecting statistical model and optimum maintenance policy: a case study of hydraulic pump.
abstract: BACKGROUND
  Proper maintenance policy can play a vital role for effective investigation of product reliability. Every engineered object such as product, plant or infrastructure needs preventive and corrective maintenance.
  
  
  METHODS
  In this paper we look at a real case study. It deals with the maintenance of hydraulic pumps used in excavators by a mining company. We obtain the data that the owner had collected and carry out an analysis and building models for pump failures. The data consist of both failure and censored lifetimes of the hydraulic pump.
  
  
  RESULTS
  Different competitive mixture models are applied to analyze a set of maintenance data of a hydraulic pump. Various characteristics of the mixture models, such as the cumulative distribution function, reliability function, mean time to failure, etc. are estimated to assess the reliability of the pump. Akaike Information Criterion, adjusted Anderson-Darling test statistic, Kolmogrov-Smirnov test statistic and root mean square error are considered to select the suitable models among a set of competitive models. The maximum likelihood estimation method via the EM algorithm is applied mainly for estimating the parameters of the models and reliability related quantities.
  
  
  CONCLUSIONS
  In this study, it is found that a threefold mixture model (Weibull-Normal-Exponential) fits well for the hydraulic pump failures data set. This paper also illustrates how a suitable statistical model can be applied to estimate the optimum maintenance period at a minimum cost of a hydraulic pump.
authors.affiliation: Department of Statistics, Pabna University of Science and Technology, Pabna, Bangladesh.
authors.forename: S
authors.initials: S
authors.lastname: Ruhi
authors.affiliation: Department of Statistics, University of Rajshahi, Rajshahi, 6205 Bangladesh.
authors.forename: M R
authors.initials: MR
authors.lastname: Karim
keywords: Case study; EM algorithm; Hydraulic pumps; Maintenance data; Mixture models; Reliability