Selecting a slurry pump goes far beyond looking at a basic flow and head curve. When handling abrasive solids, relying on clean-water pump sizing methods will almost certainly lead to premature wear, pipeline blockages, or unexpected motor overloading. The fluid dynamics change entirely once you introduce solid particles, high concentrations, and fluctuating slurry densities.
This guide is designed for procurement managers, EPC engineers, and project leaders managing mineral processing, sand and gravel extraction, coal preparation, power generation, and industrial slurry transfer projects. You need to account for particle size distribution, slurry rheology, pipeline velocity, and material compatibility to find the exact match for your site conditions. We will walk you through the precise technical steps required to finalize your pump specifications and prepare a high-quality Request for Quotation (RFQ).
Key Takeaways
- Sizing requires a deep understanding of your slurry: specific gravity, solids concentration, and particle size distribution (d50/d85).
- Clean-water performance curves must be derated to account for slurry density and viscosity.
- Pipeline velocity dictates your operating point; running too slow causes settling, while running too fast accelerates wear.
- Wet-end material selection (alloy vs. rubber) depends on particle sharpness, impact force, and chemical compatibility, not just upfront cost.
- Oversizing a pump for “safety margins” pushes the operating point off the Best Efficiency Point (BEP), causing internal recirculation and rapid component destruction.
Quick Answer: How Do You Select a Horizontal Slurry Pump?
You can narrow down the right horizontal slurry pump by following a strict sequence of hydraulic and mechanical evaluations. Skipping any of these steps compromises the entire pumping system.
First, establish the minimum, normal, and maximum flow rates your process demands. Next, calculate the total dynamic head (TDH) by factoring in static elevation, pipeline friction, and discharge pressure requirements. Simultaneously, you must gather precise data on solids concentration and slurry density, as these figures directly dictate motor sizing and power draw.
Once the hydraulics are mapped, look at the physical solids: determine the maximum particle size, overall distribution, shape, and hardness. Check the fluid’s pH and temperature to assess corrosion risks. With these parameters locked in, you apply slurry correction factors to adjust the pump’s required head, efficiency, and power. Only then do you select the pump frame size, operating speed, and wet-end materials. Finally, verify the suction conditions, shaft seal requirements, and maintenance access.
Horizontal Slurry Pump Selection Input
| Selection Item | Required Project Data | Effect on Pump Selection |
| Flow rate | Minimum, normal and maximum flow | Pump size and operating range |
| Total head | Static head, pipe losses and discharge pressure | Impeller diameter and pump speed |
| Solids concentration | Percentage by weight or volume | Slurry density, wear and power |
| Particle size | Typical size, maximum size and distribution | Impeller passage and material |
| Slurry density | Mixture SG and solids SG | Motor power and shaft loading |
| Abrasiveness | Particle hardness, shape and mineral type | Wet-end material and pump speed |
| Chemistry | pH, temperature and corrosive components | Alloy, rubber and seal compatibility |
| Operating conditions | Hours, starts, suction level and maintenance plan | Seal, drive and spare parts |
TIP: Prepare your complete slurry and pipeline data before requesting a quotation. A recommendation based solely on flow and head is only a preliminary estimate.
When Is a Horizontal Slurry Pump the Right Choice?
A horizontal slurry pump is a dry-mounted centrifugal pump where the casing and drive assembly sit completely outside the sump or fluid source. Because the pump remains accessible on the floor or foundation, maintenance teams can easily inspect seals, adjust bearings, and replace heavy wet-end components without requiring complex lifting gear over an open pit.
This configuration fits perfectly into demanding industrial applications. Typical duties include mill discharge circuits, hydrocyclone feeding, thickener underflow, tailings transfer, and heavy wash-plant circulation. If your project involves high flow rates, extreme discharge pressures, or highly abrasive materials that necessitate frequent liner replacements, the dry-mounted horizontal design provides the highest mechanical stability and maintenance convenience.
Horizontal vs Vertical and Submersible Slurry Pumps
Different site layouts demand different pump configurations. Your installation space, sump depth, and maintenance capabilities dictate which structural design makes sense.
Pump Configuration Comparison
| Pump Configuration | Installation | Main Advantage | Main Limitation |
| Horizontal slurry pump | Dry-mounted beside the sump | Wide selection range and accessible maintenance | Requires suitable suction conditions |
| Vertical slurry pump | Mounted over a sump or tank | No conventional horizontal suction pipe | Limited by installation depth and arrangement |
| Submersible slurry pump | Motor and pump submerged | Compact installation and mobile operation | Maintenance requires pump removal |
Suitable Duties and Selection Limits
You should never default to a horizontal frame simply because you have a high flow requirement. Several operating conditions demand closer engineering review before finalizing a dry-mounted setup.
Evaluate the system further if your project involves:
- Severe fluctuations in the suction liquid level.
- Inadequate Net Positive Suction Head available (NPSHa).
- Fast-settling slurries combined with long, horizontal suction lines.
- Heavy froth, entrained air, or highly viscous mining foams.
- Oversized tramp material or severely irregular particle shapes.
- Extreme high-temperature fluids or highly toxic chemicals.
- Sites entirely lacking clean gland sealing water for traditional packing.
Define the Slurry Before Selecting the Pump
Labeling your medium as “slurry” gives the manufacturer almost zero usable engineering data. A slurry is a highly complex two-phase fluid. To specify the right equipment, the factory needs a detailed breakdown of the carrier liquid, the solid particles, the volumetric concentration, and the chemical environment.
Slurry Property and Selection Effect
| Slurry Property | Buyer Should Provide | Why It Matters |
| Carrier liquid | Water, chemical solution or process liquid | Determines corrosion and seal compatibility |
| Solids type | Ore, sand, coal, ash, lime or other solids | Indicates abrasion and settling behavior |
| Solids concentration | Weight percentage or volume percentage | Changes density, friction and power |
| Particle distribution | d50, d85 and maximum size if available | Affects passage size and wear pattern |
| Particle shape | Rounded, angular, sharp or fibrous | Affects impact and cutting wear |
| Slurry density | kg/m³ or specific gravity | Affects motor and hydraulic selection |
| pH and chemistry | Normal and upset values | Determines wet-end material |
| Temperature | Minimum and maximum | Affects rubber, seals and bearings |
| Rheology | Settling or non-settling, Newtonian or non-Newtonian | Affects pipeline and pump calculations |
Solids Concentration, Density, and Rheology
You must clearly distinguish between solids concentration by weight (Cw) and concentration by volume (Cv). Mixing these up completely alters the specific gravity (SG) calculations. As the mixture density rises, the pump requires exponentially more shaft power to move the fluid.
High-concentration slurries dramatically increase internal friction. When you exceed certain volumetric thresholds, the slurry transitions from a settling mixture to a non-settling, non-Newtonian fluid. At this stage, the fluid behaves more like a paste. You cannot use the same hydraulic formulas for a thick paste as you do for a fast-settling silica sand slurry. If you only supply water-equivalent flow numbers, the resulting pump will fail to move the actual heavy slurry.
Particle Size, Shape, and Abrasiveness
Providing just the “maximum particle size” limits the engineering team’s ability to optimize the pump. A few large rocks require a wide impeller passage, but the vast majority of the wear comes from the bulk of the material. Supplying a full size distribution—specifically the d50 (median size) and d85—paints an accurate picture of the wear pattern.
Particle shape directly dictates the wear mechanism. Smooth, rounded river gravel causes sliding abrasion, while crushed, angular hard-rock ore causes severe impact and cutting wear. These factors dictate your required impeller geometry, the operating speed limits, and the specific hardness of the metallurgy required to survive the duty cycle. Large particles also introduce the risk of severe vibration if they become momentarily lodged inside the volute.
pH, Temperature, and Corrosion Risk
Abrasion and corrosion frequently occur at the same time, severely compounding metal loss. As abrasive particles strip away the protective oxidized layer on metal surfaces, the exposed fresh metal immediately corrodes, only to be stripped away again.
High-chrome alloys deliver exceptional resistance to sliding abrasion, but they fail rapidly in highly acidic environments (low pH). Rubber lining handles fine abrasives beautifully but degrades, blisters, or melts if the carrier liquid temperature exceeds its specific thermal limits, or if tramp oils and hydrocarbons are present. For complex chemical slurries, you might need to specify duplex stainless steels, engineered ceramics, or specialty elastomers. Never select wet-end materials purely based on upfront purchase costs.
TIP: Always verify the exact chemical composition of the carrier liquid. Trace amounts of unexpected chemicals—like flotation reagents or stray chlorides—can destroy standard elastomers in weeks.
Calculate Flow, Total Dynamic Head, and Slurry Pipeline Requirements
Getting the hydraulics right is the foundation of slurry pump selection. Without accurate pipeline data, any pump recommendation remains a guess.
Required Flow and Operating Range
Provide a complete operating range rather than a single, static design point. The manufacturer needs to know your minimum expected flow, the normal daily operating flow, and the absolute maximum flow.
Clarify your continuous versus intermittent operating hours. Tell the supplier how many duty pumps will run simultaneously and how many standby units you plan to install. If your plant plans to increase capacity in two years, state the future capacity allowance now. Buying a pump sized exclusively for today’s flow might lock you out of a cheap impeller upgrade later.
Static Head and Slurry Pipeline Losses
You calculate Total Dynamic Head (TDH) by adding up three distinct components:
TDH = Static Head + Pipeline Friction Loss + Fittings and Valve Losses + Required Discharge Pressure
To calculate this properly, document the exact vertical elevation difference between the suction liquid level and the final discharge point. Map out the entire pipe run: total length, internal diameter, material type, and the exact count of long-radius bends, isolation valves, and changes in direction. If the line features a residual discharge pressure requirement (such as feeding a pressurized filter press or a hydrocyclone battery), this must be added to the TDH. Never copy a friction loss calculation from a clean-water system—heavy slurries generate significantly higher friction.
Pipeline Velocity, Settling Risk, and Slurry Corrections
Slurry pipelines must maintain a highly specific fluid velocity. Drop the speed too low, and solids will immediately settle on the bottom of the pipe, reducing the internal diameter and eventually blocking the line entirely. Push the velocity too high, and the friction skyrockets, wasting massive amounts of electricity and chewing through both the pipe walls and the high head slurry pump components.
Your pipeline must operate above the critical settling velocity. This minimum speed shifts based on pipe diameter, solid specific gravity, and particle size. Long horizontal runs with low points require special attention to prevent sanding during shutdown procedures. Because slurry behaves differently than water, the manufacturer will apply derating factors (often called HR and ER) to lower the pump’s clean-water head and efficiency capabilities to match the reality of the heavy fluid.
Select Pump Size, Speed, and Operating Point
Once you have the corrected head and flow targets, you can map them against the manufacturer’s performance curves to find the physical frame size and optimal running speed.
Best Efficiency Point and Preferred Operating Range
Every centrifugal pump has a Best Efficiency Point (BEP)—the flow rate where fluid moves through the casing with the least amount of turbulence. For severe slurry duties, you want your normal operating point to fall directly around this BEP. Check HI slurry pump standards to understand acceptable operating windows for heavy-duty applications.
If you force a pump to run too far to the left of BEP (low flow), fluid recirculation occurs inside the casing, aggressively scouring the impeller eye and cutwater. If you run too far to the right (high flow), you risk cavitation, severe vibration, and overloading the shaft bearings. Never select an oversized pump just to secure a “safety margin.” An oversized pump running at partial capacity will destroy itself much faster than a correctly sized pump working at its design point.
Pump Speed, Impeller Diameter, and Wear Rate
Rotational speed is the absolute biggest driver of wear. Wear rates in slurry pumps increase exponentially with speed—often to the third power. Doubling your pump speed can increase the wear rate by a factor of eight.
Therefore, a larger pump running at a slow speed will significantly outlast a smaller pump running at high speed to achieve the same flow and head. While the small, high-speed pump looks cheaper on the initial procurement spreadsheet, the frequent downtime and massive spare parts consumption will destroy your operating budget. The selected impeller diameter must clear your maximum particle size, and the final RPM must leave enough torque margin on the motor shaft to handle temporary spikes in slurry density.
Choose Wet-End Materials and Replaceable Wear Parts
The casing, impeller, and liners act as the primary defense against the slurry. You need to match the metallurgical or elastomeric properties directly to the particle behavior and fluid chemistry.
Wet-End Material Options
| Wet-End Option | Suitable Selection Direction | Main Points to Check |
| High-chrome alloy | Hard, coarse or highly abrasive particles | Hardness, impact, corrosion and operating speed |
| Rubber lining | Fine particles and compatible chemical conditions | Particle sharpness, temperature and chemical compatibility |
| Stainless or duplex steel | Combined corrosion and moderate solids | Chlorides, pH, temperature and erosion |
| Special alloy or ceramic | Severe combined wear or chemical service | Cost, brittleness, availability and repairability |
| Polyurethane or other elastomer | Selected fine-particle or specific chemical duties | Temperature, particle size and elastomer compatibility |
High-Chrome Alloy Wet Ends
White irons and high-chrome alloys offer exceptional hardness, making them the standard choice for aggressive rock, coarse ores, and sharp sands. When specifying a high chrome alloy pump, you ensure the impeller, volute liners, and throatbush can withstand relentless high-velocity impacts. However, standard high-chrome does not tolerate highly acidic conditions. If your slurry is corrosive, you will need specialized alloy variations with adjusted chromium and molybdenum levels.
Rubber-Lined Construction
A rubber lined slurry pump absorbs the kinetic energy of small particles. Instead of cutting into the surface, fine particles bounce off the resilient elastomer. You should specify a rubber lined pump for cyclone feeds, fine tailings, and mineral sands under 5mm in diameter. However, you must verify the exact rubber grade against the fluid temperature and tramp chemicals. Sharp, oversized tramp metal will easily slice through standard natural rubber, leading to rapid liner failure.
Special Materials for Combined Abrasion and Corrosion
When dealing with flue gas desulfurization (FGD), acidic leach circuits, or high-chloride environments, neither standard chrome nor natural rubber will survive. In these cases, you evaluate duplex stainless steels, engineered polyurethanes, or advanced ceramic coatings. Upgrading the material can buy you extra operating months, but no material in the world can compensate for a poorly sized pump running way off its BEP or dealing with severe cavitation.
Select the Impeller, Casing, Shaft Seal, and Drive
Beyond the wet-end materials, the mechanical configuration of the pump determines how easily your maintenance team can keep the system online.
Impeller Passage and Casing Design
The internal geometry of the impeller dictates your solids handling limit. An impeller with three or four heavy vanes passes large rocks easier but may sacrifice a few points of hydraulic efficiency compared to a five-vane design.
Look closely at the casing structure. A double-casing design (an outer ductile iron shell holding an inner wear liner) provides catastrophic pressure protection. If the inner liner wears through, the outer shell prevents high-pressure slurry from blasting into the plant. Evaluate the thickness of the replaceable liners and verify if the pump features external impeller adjustment. Moving the impeller forward as it wears helps recover lost efficiency and extends the maintenance interval.
Gland Packing, Expeller, or Mechanical Seal
Shaft sealing keeps the slurry inside the pump and protects the bearing assembly.
Seal Type Comparison
| Seal Type | Main Advantage | Selection Concern |
| Gland packing | Simple and widely serviceable | Requires correct adjustment and often seal water |
| Expeller or dynamic seal | Can reduce external sealing-water demand | Performance depends on speed and operating condition |
| Mechanical seal | Better leakage control | Requires correct material, flushing and slurry-specific design |
Standard gland packing remains popular because it is predictable and easy to repack, but it requires a constant supply of clean, high-pressure gland water to flush abrasives away from the shaft sleeve. If clean water is scarce or product dilution is forbidden, a centrifugal expeller (dynamic seal) uses a secondary spinning rotor to push slurry away from the shaft during operation. For toxic or highly corrosive duties, heavy-duty mechanical seals provide zero-leakage performance but require strict adherence to operating procedures.
Direct Drive, Belt Drive, and VFD
Direct coupling the motor to the pump creates a compact, rigid footprint ideal for fixed-speed operations. However, belt drives (V-belts) remain dominant in the mining sector because they allow operators to easily change the pump speed by swapping out a sheave.
If your process flow fluctuates constantly, integrating a Variable Frequency Drive (VFD) offers precise control. When utilizing a VFD, you must strictly monitor the lower speed limits; dropping the speed too far will cause the pipeline velocity to crash below the critical settling point, plugging the system. Always verify that the motor is rated for VFD use and sized for the absolute maximum slurry density expected during an upset condition.
Plan Suction Layout, Installation, Maintenance, and Spare Parts
The best heavy duty slurry pump will fail rapidly if bolted to a poorly designed piping layout.
Keep your suction line as short and straight as physically possible. Size the suction pipe based on the required fluid velocity, not just by matching the pump’s inlet flange size. Ensure the pipe drops smoothly into the pump without high points that trap air. Never use the pump casing to support the weight of the pipe; all piping must be independently supported.
When pouring the foundation, ensure the baseplate is properly grouted and laser-aligned. Leave ample physical clearance around the pump so technicians can pull the wet end and bearing assembly without tearing down adjacent structures. Install overhead lifting points rated for the heaviest casing components, and design flushing lines to clean the system out before shutdowns.
Recommended Spare Parts
| Recommended Spare Part | Why It Should Be Considered |
| Impeller | Major hydraulic wear component |
| Volute liner or casing | Exposed to continuous abrasive flow |
| Throatbush or suction liner | Often experiences concentrated inlet wear |
| Frame plate liner | Required for planned wet-end overhaul |
| Shaft sleeve | Protects the shaft near the seal area |
| Packing or seal kit | Required for leakage control |
| Bearings | Useful for remote or continuous-duty sites |
| Gaskets and O-rings | Required during pump disassembly |
| Fasteners and adjustment components | Reduce maintenance delays |
TIP: Evaluate the total cost of ownership over a 3-to-5 year window. A cheaper initial pump often hides expensive, proprietary spare parts and long maintenance downtime requirements.
Horizontal Slurry Pump Selection by Application
Every industry challenges a slurry pump in a completely different way. Sizing a pump for a coal wash plant requires different priorities than sizing one for a highly acidic copper tailings line.
Application Selection Matrix
| Application | Main Slurry Challenge | Selection Priority |
| Mill discharge | High density and severe abrasion | Heavy wet-end sections, power and wear life |
| Hydrocyclone feed | Stable pressure and abrasive solids | Operating point, speed and pressure capability |
| Tailings transfer | Long pipelines and settling risk | Pipeline velocity, system curve and materials |
| Sand and gravel | Coarse and abrasive particles | Large passage and impact-resistant wet ends |
| Coal washing | Variable concentration and abrasive fines | Operating range and material compatibility |
| Fly ash or bottom ash | Fine solids and possible chemical corrosion | Material, sealing and flushing |
| Chemical slurry | Combined abrasion and corrosion | Chemical compatibility and leakage control |
| Construction slurry | Variable solids and site conditions | Robustness, maintenance and installation flexibility |
When moving heavy rock out of a SAG mill, the ore slurry transfer pump handles severe impact forces, requiring thick high-chrome liners and oversized shafts. Conversely, a tailings transfer pump pushes fine, settled materials over several kilometers; the focus here shifts to maintaining pipeline velocity and handling multi-stage pressure ratings. In a prep plant, a coal washing slurry pump sees wildly variable concentrations, demanding a broad operating range and excellent shaft sealing to handle the abrasive fines.
Horizontal Slurry Pump RFQ Checklist
To get a precise, binding quotation from a manufacturer, your RFQ must contain complete system data. Missing information forces the factory to make assumptions, which ultimately transfers the operational risk back to you. Use this checklist to build your request. Require the manufacturer to provide tests in line with ISO 9906 pump testing guidelines.
- Pumped liquid and solids description
- Required minimum, normal and maximum flow
- Required total dynamic head or complete pipe route
- Solids concentration by weight or volume
- Slurry mixture density or specific gravity
- Solid particle specific gravity
- Particle size distribution, d50, d85 and maximum size
- Particle shape and hardness
- Slurry pH and chemical composition
- Minimum and maximum temperature
- Viscosity or rheological data
- Suction tank level and available NPSH
- Pipe diameter, length, elevation and fittings
- Continuous or intermittent operating hours
- Number of starts per hour
- Site altitude and ambient temperature
- Power supply, voltage and frequency
- Preferred wet-end material
- Shaft-seal and sealing-water conditions
- Required standards, inspection and testing
- Duty and standby pump arrangement
- Required spare parts
- Required documents and performance curves
- Installation location and maintenance space
Send the complete slurry and pipeline data with your RFQ. A model recommendation based only on flow and head should be treated as preliminary.
Common Horizontal Slurry Pump Selection Mistakes
Avoiding basic engineering traps saves significant downtime and capital expenditure. Review this list to ensure your procurement process stays on track.
- Selecting the pump from flow and head alone: Results in rapid wear, motor failure, or the complete inability to move heavy solids.
- Using the clean-water curve without slurry correction: Leads to undersized motors and falling short of the required discharge pressure.
- Providing only the maximum particle size: Masks the true wear pattern caused by the bulk of the d50/d85 particles, leading to poor material selection.
- Confusing solids concentration by weight and by volume: Skews the slurry density calculations entirely, resulting in massive motor sizing errors.
- Ignoring pipeline settling velocity: Causes the pipeline to plug, requiring heavy machinery to dig up and clean out the lines.
- Selecting an oversized pump for additional safety: Forces the pump to run off the BEP, causing internal recirculation, vibration, and ruined bearings.
- Operating at unnecessarily high speed: Multiplies the wear rate exponentially; the pump consumes liners and impellers at a brutal pace.
- Choosing materials only by purchase price: Cheap standard alloys melt in acidic conditions, while cheap rubber gets shredded by sharp rocks.
- Ignoring suction conditions and NPSH: Triggers cavitation, which sounds like pumping gravel and rapidly destroys the impeller eye.
- Using a standard mechanical seal without slurry review: Leads to immediate seal face destruction and catastrophic slurry leakage into the bearing housing.
- Failing to confirm motor power at maximum slurry density: Causes the motor to trip or burn out during system upsets when density spikes.
- Ordering no wear parts with the original pump: Guarantees extended downtime during the first inevitable maintenance cycle while waiting on factory shipments.
Frequently Asked Questions About Horizontal Slurry Pump Selection
FAQ 1: What is a horizontal slurry pump?
It is a heavy-duty centrifugal pump configured with a horizontal shaft, dry-mounted entirely outside the fluid. The wet-end parts are significantly thicker, more robust, and highly wear-resistant compared to standard water pumps, allowing for continuous transport of abrasive solids while offering easy maintenance access.
FAQ 2: How do you size a horizontal slurry pump?
You start by defining the flow rate, calculating the total dynamic head (TDH), and mapping the pipeline system. Then, you acquire exact slurry density, solids concentration, and particle size data. You apply slurry correction factors to the clean-water curves to find the precise operating speed, frame size, and motor power required.
FAQ 3: What information does a manufacturer need to select a slurry pump?
Provide the carrier liquid details, required flow range, static head, pipe route, solids concentration (by weight or volume), slurry specific gravity, particle size distribution, pH, temperature, and your expected daily operating hours.
FAQ 4: Can a clean-water pump curve be used for slurry selection?
A clean-water curve only serves as the preliminary baseline. You must apply head and efficiency derating factors based on the specific gravity and concentration of your slurry to predict how the pump will actually perform on-site.
FAQ 5: How does slurry density affect motor power?
As the specific gravity of the slurry increases, the pump must do significantly more physical work to move the heavier mass. The required shaft power rises in direct proportion to the fluid’s specific gravity, meaning you need a much larger motor than a water pump would require.
FAQ 6: Is high-chrome alloy or rubber lining better?
Neither is universally better; they serve different conditions. High-chrome handles sharp, coarse rocks and severe impact, provided the pH remains relatively neutral. Rubber lining excels at bouncing away fine, sliding abrasives but will tear if exposed to oversized tramp metals or high temperatures.
FAQ 7: How does pump speed affect slurry pump wear?
Wear rates increase exponentially with rotational speed. A pump running at a lower RPM with a larger impeller will experience drastically less internal wear than a smaller pump spinning quickly to achieve the same flow rate.
FAQ 8: How can solids settling in the pipeline be prevented?
You maintain fluid velocity above the critical settling limit by sizing your pipe diameter correctly against your flow rate. Additionally, you avoid running the pump at excessively low speeds on a VFD, design pipes without low trapping points, and implement clear flushing procedures during shutdown.
FAQ 9: Should you choose a horizontal, vertical, or submersible slurry pump?
Choose a horizontal pump when you have dry installation space next to the sump and need maximum maintenance convenience. Choose a vertical cantilever pump if space is tight and you want to avoid suction piping. Choose a submersible if the pump must operate underwater or requires constant relocation.
FAQ 10: Which spare parts should be ordered with a horizontal slurry pump?
Always stock a spare impeller, volute liner (or casing liners), throatbush, shaft sleeve, and a complete set of bearing seals, gaskets, and gland packing. Having these on the shelf prevents minor wear issues from causing massive plant-wide downtime.
