What is a slurry pump?
A slurry pump is a centrifugal pump that transports liquids containing highly abrasive solids. The pump is designed with hard surfaces on the wetted area to prevent wear due to the abrasive solids. Due to the high fluid pressure generated inside the pump, mechanical seals are used to prevent leakage. The pump runs at high speeds (RPMs) to create centrifugal force. This force helps to add pressure and velocity to the pumped content.
There is a component known as an impeller mounted on the pump shaft. The impeller has vanes that create centrifugal force when the pump is turned on. One of the critical features of this pump is greater mechanical strength and power relative to standard pumps. Also, these pumps are large and are made of more rugged shafts and bearings. Applications of this pump include mining, coal, food processing, petrochemicals, and construction, among others.
Figure: Slurry pump.
What is a mechanical seal?
A mechanical seal is a machine element that prevents fluid leakage where a shaft rotates within a stationary casing. The seal allows the shaft to rotate while ensuring no fluid leaves the pump except through the discharge port.
How to extend mechanical seal life on slurry pumps
Sufficient lubrication
Lubrication on the bearings and coupling helps to reduce heat on power transmission elements like the shaft and bearings. If the pump lacks lubrication, heat generated moves to the mechanical seals, causing deformation and, thus, failure. Perform frequent visual checks to confirm enough lubrication on bearings and couplings.
Prevent dry running
Dry running in pumps means operating the pump without fluid. Slurry pump manufacturers design pumps such that the pumped fluid also helps in cooling. As such, when the pump operates without the liquid, a lot of heat is generated. The heat is transferred to the mechanical seals, causing damage and, thus, pump failure. Enhance mechanical seal life by ensuring the pumped fluid is not below the stated minimum flow rate for the pump.
Prevent chemical attack
Suppose the mechanical seal is incompatible with the pumped liquid; the fluid attacks the seal, causing leakage. It is advisable to understand the properties of the fluid before purchasing the pump and mechanical seals. This will help buy a pump whose materials can resist chemical attack and thus save the seals. Fluid leakage, especially corrosive and flammable liquids, can cause severe damage to the pump operator and environment, causing legal action and, thus, heavy fines.
Prevent cavitation
Cavitation is the formation and implosion of vapor bubbles in the pump when the bubbles reach an area of high pressure. When the bubble implodes, it releases a lot of energy that causes damage to the impeller and increases the pump temperature. The high temperatures cause mechanical seals to fail. There are various causes of cavitation. Determine the specific cause of to help address this problem.
Do not exceed the fluid temperature.
Slurry pump manufacturers design the pump to transport fluid within a specific temperature range. If the fluid temperatures exceed the pump limits, it heats the seal elastomers, causing swelling or melting. Eventually, the seals start leaking.
Proper installation
Mechanical seals are meant to move with the shaft. Seals are subject to vertical and lateral movement. If poorly installed, the excess play causes forces that damage the seals. Also, if the seal is too restricted, its springs snap and wear out. Follow the slurry pump manufacturer’s instructions to ensure proper installation.
Ensure bearings are in good condition.
Worn-out bearings create a lot of play for the shaft. The play causes lateral movement, which the seal absorbs and thus leads to wear and tear.
Ensure the shaft is in good working condition.
Some seal materials, such as Viton, intensify shaft wear. As such, when a seal is replaced with a new one, the shaft will have a smaller outside diameter, and thus, the seal will not fit, causing fluid leakage. By having a good shaft, this problem will not occur, and therefore, the seal will have a long service life.
Remove foreign materials
If foreign materials like dirt and dust get into the seals, for example, during installation, they reduce the integrity of the seal. As such, ensure no dirt, dust, or any other foreign material interferes with the surfaces of the mechanical seals to help prevent failure and leakage.
Signs that slurry pump mechanical seals are about to fail
- The pump produces a popping or squealing sound. This means the pump does not have enough fluid to lubricate the seal faces.
- Seals have uneven wear track due to being too tight.
- Cracked or fractured seal face to thermal shock or mechanical impact.
- Carbon dust accumulates on the outside surface of the seal.
- The seal has notches or grooves.