I. Selection and Installation of Slurry Pumps

Slurry pumps shall be selected in accordance with the characteristics of the liquid being conveyed, and their required performance shall be verified by analyzing suction and discharge conditions, as well as whether the operation is intermittent or continuous. Slurry pumps should generally be operated at or near the pressure and flow conditions specified in the manufacturer’s design data. During pump installation, the following checks shall be carried out:
1. The dimensions, location, and elevation of the foundation shall comply with the design requirements; anchor bolts must be properly and securely embedded in the concrete foundation; and the equipment shall be free from missing parts, damage, or corrosion.
2. Based on the characteristics of the fluid being conveyed by the pump, the materials of the principal components, shaft seals, and gaskets shall be verified as necessary.
3. The leveling and alignment of pumps shall comply with the provisions of the equipment’s technical documentation; where no such provisions exist, they shall comply with the current national standard “General Code for Construction and Acceptance of Mechanical Equipment Installation Projects.”
4. The installation of all piping and pipe fittings connected to the pump casing, as well as the cleaning requirements for lubricating oil pipelines, shall comply with the relevant national standards.

II. Operation of Slurry Pumps

The pump’s trial run shall comply with the following requirements. ：
1. The rotation direction of the drive motor shall be the same as that of the pump;
2. Determine the rotation direction of pipeline pumps and coaxial pumps;
3. All fixed connection points shall be free from looseness, and the specifications and quantities of lubricant applied to all lubrication points shall comply with the provisions of the equipment’s technical documentation.
4. Parts requiring pre-lubrication shall be pre-lubricated in accordance with the specified requirements.
5. All indicating instruments and safety protection devices shall be sensitive, accurate, and reliable.
6. The turning gear shall operate smoothly with no abnormal conditions;
7. Prior to trial operation, the high-temperature pump shall be preheated, with a uniform temperature rise not exceeding 500°C per hour; the temperature difference between the pump casing surface and the process piping at the working medium inlet shall not exceed 40–90°C.
8. Install a connection device to eliminate the effects of temperature rise, and install a bypass connection device to supply cooling water.
The following points should be observed when operating a slurry pump: ：
1. Do not operate the pump without water; do not adjust the suction inlet to reduce the flow rate; and do not operate at excessively low flow rates.
2. Monitor the operating process to completely prevent packing gland leakage; when replacing the packing gland, use new packing material.
3. Ensure that the mechanical seal is adequately flushed with water; do not use excessive water flow when water-cooling the bearings.
4. Do not use excessive lubricant;
5. Perform inspections at the recommended intervals. Maintain operational records that document operating hours, packing adjustments and replacements, lubricant additions, and other maintenance activities and their corresponding schedules. Regularly measure and record the slurry pump’s suction and discharge pressures, flow rate, input power, flushing fluid and bearing temperatures, as well as vibration levels.

III. Maintenance of Slurry Pumps

1. Analysis of Mechanical Seal Failure in Slurry Pumps
The shutdown of slurry pumps is primarily caused by mechanical seal failure. The most common manifestation of such failure is leakage, which can be attributed to the following causes:
(1) Leakage at the sealing faces of the rotating and stationary rings is mainly caused by the following factors: the end-face flatness and roughness do not meet the specified requirements, or the surface is scratched; particulate matter is present between the end faces, preventing them from running in parallel; or the installation is incomplete or improper.
(2) Leakage from the compensation ring seal is primarily caused by: deformation of the gland, non-uniform preloading force; improper installation; substandard seal quality; or incorrect seal selection.
Practical operating results show that the most common failure location for sealing elements is the end faces of the rotating and stationary rings. Cracking on the end faces of these rings is a typical failure mode in slurry pump mechanical seals, with the primary causes being:
(1) During installation, excessive clearance at the sealing interface prevents the flushing fluid from adequately removing the heat generated by friction between the mating surfaces; moreover, the flushing fluid leaks out through the sealing gap, leading to overheating and subsequent damage to the end faces.
(2) Vaporization and expansion of the liquid medium cause the two end faces to separate under the action of the vaporization-expansion force; when the sealing faces are forcibly brought into contact, the lubricating film is disrupted, leading to overheating of the end-face surfaces.
(3) The liquid medium has poor lubricity, and coupled with excessive operating pressure, the two sealing faces fail to track each other’s rotation in synchrony. For example, in a high-speed pump operating at 20,445 r/min with a sealing-face center diameter of 7 cm, the peripheral velocity can reach as high as 75 m/s. When one sealing face lags behind and cannot keep up with the rotation, the resulting instantaneous high temperature can lead to damage of the sealing surfaces.
(4) Clogging of the seal flushing fluid orifice plate or filter screen leads to insufficient water flow, resulting in seal failure.
In addition, surface grooves on the sealing face can lead to gaps during end-face contact, resulting in seal failure. The primary causes include:
(1) The liquid medium is contaminated with tiny, hard particles that slide at high velocity across the sealing faces, causing surface damage and leading to failure.
(2) Poor coaxial alignment of the pump’s drive components causes the end faces to be subjected to one instance of wobbling and friction per pump revolution after startup, resulting in an eccentric running trajectory of the rotating seal face. This leads to vaporization at the end faces and subsequent overheating-induced wear.
(3) Frequent changes in the hydraulic characteristics of the liquid medium induce pump vibration, leading to misalignment of the sealing surfaces and subsequent failure.
Corrosion of sealing elements by liquid media, stress concentration, mismatch between soft and hard materials, erosive wear, incompatibility of auxiliary seals such as O-rings, V-rings, and groove rings with the liquid medium, and deformation can all lead to surface damage and failure of mechanical seals. Therefore, a comprehensive analysis of the failure modes is essential to identify the root causes and ensure the long-term reliable operation of mechanical seals.
2. Requirements after the slurry pump is shut down
(1) After the slurry pump is shut down, the pump’s inlet valve shall be closed; once the pump has cooled, the valves of the auxiliary systems shall be closed in sequence.
(2) Shutdown of high-temperature pumps shall be carried out in accordance with the provisions of the equipment technical documentation. After shutdown, the pump shaft shall be manually turned half a revolution every 20 to 30 minutes until the pump casing temperature drops to 50°C.
(3) When a cryogenic pump is shut down, and unless otherwise specified, the pump casing shall be kept continuously filled with liquid; the suction valve and discharge valve shall remain normally open; for cryogenic pumps equipped with double-end mechanical seals, the liquid-level controller and the seal fluid in the pump seal chamber shall maintain the pump’s priming pressure.
(4) For pumps conveying media that are prone to crystallization, solidification, or sedimentation, prevent blockage after shutdown and promptly flush the pump and piping with clean water or other suitable media. ⑤ Drain any liquid accumulated inside the pump to prevent rusting and freezing-induced cracking.
3. Storage of Slurry Pumps
(1) Pumps that have not yet been installed shall have their unpainted surfaces coated with a suitable rust inhibitor; oil-lubricated bearings shall be fully filled with the appropriate lubricating oil, while grease-lubricated bearings shall be greased exclusively with a single type of grease—mixed greases are prohibited.
(2) For a short period, pump clean liquid to flush, purge the suction line, discharge line, pump casing, and impeller, and then completely drain the flushing fluid from the pump casing, suction line, and discharge line.
(3) Drain all the oil from the bearing housing, then refill with clean oil; thoroughly clean out the old grease and replenish with new grease.
(4) Seal the inlet and outlet ports, store the pump in a clean, dry location to protect the motor windings from moisture, and spray the interior of the pump casing with rust-inhibiting and corrosion-preventing fluid.
(5) Rotate the pump shaft once a month to prevent freezing, and lubricate the bearings.