DD Washer Maintenance & Lifecycle Services

Maximise the performance and service life of your DD Washers

PR Rolls provides comprehensive on-site DD Washer maintenance, repair, refurbishment and lifecycle services for pulp mills worldwide. Our experienced field service engineers support customers throughout the entire life of their DD Washers—from production inspections and annual shutdown maintenance to major overhauls, retrofit projects and equipment modernization.

DD Washers are among the most important process units in a pulp mill. Their performance directly affects washing efficiency, pulp quality, chemical consumption and production reliability. Wear on seals, sealing faces and other critical components gradually reduces performance and increases operating costs if maintenance is delayed.

PR Rolls helps mills maximise equipment availability through structured maintenance programmes, engineered upgrades and high-quality spare parts, enabling longer service intervals and predictable shutdown planning.

Complete on-site DD Washer Lifecycle Services

PR Rolls has developed a structured maintenance concept that supports every stage of a DD Washer's operational life. Rather than reacting to failures, we help mills maintain performance through preventive maintenance and lifecycle planning.

Our service concept consists of five maintenance stages:

Production Inspection
Standard Maintenance
Extended Maintenance
Major Overhaul
Complete Retrofit

Each stage is tailored to the condition of the equipment and the customer's maintenance strategy, ensuring that the right work is carried out at the right time.

Why DD Washer Maintenance Matters

A properly maintained DD Washer contributes to:

Higher washing efficiency
Improved pulp quality
Lower chemical consumption
Reduced water consumption
Increased equipment availability
Reduced leakage
Longer service life
Lower maintenance costs
More predictable shutdown planning

By maintaining critical components before failures occur, mills can minimise production losses and maximise the lifetime of existing equipment.

Stage 1 – Production Inspection

Assess equipment condition before the shutdown
PR Rolls recommends carrying out a production inspection approximately 4–6 months before a planned shutdown. This allows sufficient time for engineering, spare parts preparation and maintenance planning.

During the inspection, our specialists evaluate the overall condition and performance of the DD Washer.

Typical inspection activities include:

Washing performance assessment
Seal condition inspection
Leakage inspection
Pneumatic seal pressure verification
Seal water flow measurements
Filtration tube inspection
Element gear inspection
Cake release evaluation
Review of maintenance history
Shutdown planning recommendations

Following the inspection, customers receive a technical report including recommendations for maintenance, spare parts and future improvements.

Stage 2 – Standard Maintenance

Planned shutdown maintenance
Standard maintenance is normally carried out every 12–24 months depending on operating conditions and component wear.

The objective is to restore the DD Washer to reliable operating condition while preventing future failures.

Typical maintenance work includes:

Hybrid® seal replacement
T-profile replacement
Pneumatic seal replacement
O-ring replacement
Element seal replacement
Water ring inspection and replacement
Nose list replacement when required
Drum centricity measurements
Drum adjustment
Pressure plate inspection
Inspection of perforated plates
Inspection of ribs and wear components
Shower inspection and adjustment
High-pressure washing system inspection
Screw conveyor inspection
Filtration tube inspection

Routine maintenance helps maintain washing efficiency while reducing the risk of unplanned shutdowns.

PR Rolls Hybrid® DD Washer Seals

Designed for longer service intervals
PR Rolls has developed the Hybrid® DD Washer Seal to improve reliability, simplify installation and extend maintenance intervals. The seal has been developed in cooperation with universities and tested under demanding operating conditions.

Compared with conventional sealing solutions, Hybrid® seals provide:

Long service life
Easy on-site cutting and joining
Accurate installation
Reduced installation risk
Low friction characteristics
Excellent resistance to heat and process chemicals
Short delivery times
Extended maintenance intervals

Operational references demonstrate excellent performance with no measurable wear after approximately 18 months of operation.

Stage 3 – Extended Maintenance

Restore worn components
When inspections identify wear beyond routine maintenance, PR Rolls performs extended refurbishment to restore critical components and extend equipment lifetime.

Services include:

On-site machining
Thermal spray coating
Twin Wire Arc coating
Bearing housing seal replacement
Seal water pipe replacement
Surface restoration
Mechanical repairs

These services restore sealing performance without requiring replacement of major components.

Advanced Thermal Spray Coating

PR Rolls restores worn sealing surfaces using advanced thermal spray technology.

One commonly used coating material is Sanicro 28, selected for its excellent corrosion resistance and compatibility with stainless steel materials used in DD Washers.

Typical coating characteristics include:

Excellent corrosion resistance
Suitable for SMO and AISI materials
Hardness approximately 400 HV
Coating thickness between 2–7 mm
Surface finish Ra 0.4–0.5

These coatings restore worn sealing surfaces and help extend maintenance intervals.

Stage 4 – Major Overhaul

Extend equipment lifetime
Major overhauls are typically carried out after many years of operation to restore the DD Washer to optimal condition.

Typical overhaul work includes:

Drum repairs
Pressure plate refurbishment
Repair of perforated plates
Repair of ribs and support plates
Sealing bar refurbishment
Mechanical repairs
Structural inspections and possible repairs

Whenever possible, existing components are restored rather than replaced, reducing both maintenance costs and downtime.

Stellite Sealing Bars

PR Rolls has developed sealing bars with Stellite hard-facing to improve durability and reduce maintenance frequency.

Compared with conventional sealing bars, they offer:

Approximately 1.5 times longer service life
Improved resistance to wear
Reduced heat distortion
Lower lifecycle costs
Faster shutdown execution

Existing sealing bars are precision machined before new Stellite surfaces are welded into place.

Drum Repairs

PR Rolls performs comprehensive repairs on DD Washer drums, including:

Repair of perforated plates
Repair of ribs
Repair of support plates
Pressure plate refurbishment
Surface restoration
Welding repairs
Precision machining

These repairs help extend the service life of existing drums while maintaining washing performance.

Stage 5 – Complete DD Washer Retrofit

Modernise existing equipment
When a DD Washer reaches the end of its original design life, PR Rolls offers complete retrofit solutions that restore performance while extending equipment lifetime.

Retrofit projects may include:

Replacement of perforated plates
Filtrate channel machining
Suction zone machining
Pressure plate rebuilding
Corrosion repairs
Valve refurbishment
Rotating flush pipe modifications
Drum exchange during shutdown
Complete reassembly and commissioning

These projects provide a cost-effective alternative to replacing the complete washer.

Modernization Services

PR Rolls also modernises existing DD Washers to improve reliability and simplify future maintenance.

Modernization projects may include:

Hydraulic-to-electric drive conversion
Laser scanning
3D modelling
Mechanical engineering
Installation
Commissioning
Lifecycle support

These upgrades improve operational reliability while extending equipment service life.

Spare Parts for DD Washers

PR Rolls supplies high-quality spare parts for major DD Washer brands.

Our spare parts programme includes:

Hybrid® seals
T-profiles
Pneumatic seals
O-rings
Water rings
Element seals
Sealing bars
Pressure plates
Perforated plates
Ribs
Support plates

All parts are manufactured to provide reliable performance and long service life in demanding pulp mill environments.

Why Choose PR Rolls?

PR Rolls combines field service expertise with engineering knowledge and specialised repair technologies.

Our customers benefit from:

Complete DD Washer lifecycle services
Experienced field service engineers
Hybrid® sealing technology with short delivery time for sealings
On-site machining and thermal spray coating
Precision measurements
High-quality spare parts
Major overhaul capability
Retrofit and modernization projects
Global shutdown support
Financial benefit, work quality and almost zero complaints, which reduce downtime and enable an error-free operational process.
Minimization of risks, e.g. available consulting services, spare parts and maintenance security (reliable production process, safe, environmentally friendly and economical production process).
High-quality and timely maintenance ensures a long service life for the equipment (long experience and expertise in coating vs. quality, seal quality and durability). Quality maintenance reduces chemical consumption in downstream processes and thereby extends equipment reliability and lifespan. A functioning system also enables minimal fiber loss.

By combining preventive maintenance with technical improvements, PR Rolls helps pulp mills maximise equipment availability, improve washing efficiency and reduce lifecycle costs.

DD Washer Experience at a Glance

More than 20 years of DD Washer development and service experience
Long-term maintenance agreements with leading pulp producers
Hybrid® DD Washer Seals developed through continuous product development
Proven references from Europe, Asia and other international markets
On-site machining, coating and refurbishment specialists
Complete lifecycle services from inspection to total retrofit
Global field service support for planned shutdowns and major overhauls