Dry Running in Magnetic Drive Pumps: How Runsafe SiC Bushes Reduce the Risk

Magnetic drive centrifugal pumps offer reliable, leak-free operation across a wide range of demanding applications. However, like any centrifugal pump, correct operating conditions are essential – and dry running can present a significant risk of pump damage or failure.

To provide increased protection against dry-running conditions, many CDR magnetic drive pumps incorporate RunSafe Sintered Silicon Carbide (SSiC) bushes with an amorphous diamond-like carbon (aDLC) coating.

This low-friction diamond coating helps to protect the bushes in the event of poor lubrication or accidental dry running, whilst also contributing to improved efficiency and extended pump service life during normal operation.

What Causes Dry Running in Magnetic Drive Pumps?

Dry running occurs when a pump operates without an adequate supply of liquid. This can happen for several reasons, including accidental start-up without priming, loss of suction or the supply tank running empty.

When a magnetic drive pump operates without sufficient liquid, friction between internal components can cause temperatures to rise rapidly. Without protection, the resulting heat can damage the bearing surfaces, potentially leading to pump failure.

How Are CDR Magnetic Drive Pumps Protected Against Dry Running?

The use of RunSafe SSiC bushes with aDLC coating on CDR magnetic drive pumps provides additional protection against dry-running conditions.

Just a few microns thick, the aDLC coating is applied using plasma-assisted chemical vapour deposition. This coating provides an extremely hard, low-friction surface that can improve the performance of the bushes under challenging operating conditions.

The properties of the aDLC coating include:

• Amorphous and isotropic structure
• Excellent hardness (HV 0.05 4000–6000)
• Good elasticity despite high hardness
• High wear resistance
• Optimum surface qualities
• Good thermal conductivity
• Temperature resistance up to 300°C
• Broad chemical resistance
• Low coefficient of friction without lubrication (0.02–0.04)

The particularly low coefficient of friction is important during dry-running conditions, as it reduces the heat generated between the bearing surfaces and helps the pump withstand a loss of lubrication for longer before damage occurs.

RunSafe SSiC bushes are used across the following CDR magnetic drive pump ranges: ETN, UTN, UTS, XTN, XTS and DTN.

Engineering Benefits of Diamond-Coated RunSafe SSiC Bushes

The benefits of RunSafe SSiC bushes with aDLC coatings are not limited to dry-running protection. The low-friction characteristics of the coating can also contribute to the efficiency and reliability of magnetic drive pumps during normal operation, helping to reduce energy consumption and associated operating costs.

Engineering benefits include:

• Reduced friction
• Lower power consumption
• Assisted lubrication
• Coating thickness that does not affect the final component dimensions
• Ultraclean surface

These characteristics can help reduce wear on critical components, minimise downtime and extend pump service life, while providing an additional level of protection against unexpected operating conditions.

Putting RunSafe SSiC Bushes to the Test

When magnetic drive pumps are run dry, damage can occur within seconds.

To assess the performance of RunSafe SSiC bushes, dry-running tests were carried out using a UTS-B 80-50-200 magnetic drive centrifugal pump. Two configurations were tested: one using a Hastelloy C isolation shell and the other using a zirconium oxide isolation shell.

Pump model: UTS-B 80-50-200
Materials: Stainless Steel
Bushes: RunSafe SSiC

The test simulated a tank-unloading application. The pump was started normally and then allowed to continue operating after the tank had emptied, until pump failure occurred.

Test 1: Hastelloy C Isolation Shell
Result: The pump operated for 46 minutes and 30 seconds under dry-running conditions before failure.

Test 2: Zirconium Oxide Isolation Shell
Result: The pump operated for 53 minutes and 40 seconds under dry-running conditions before failure.

The zirconium oxide isolation shell reduced the temperature generated inside the pump compared with the Hastelloy C configuration. This helped prevent complete vaporisation of the remaining liquid, allowing some lubrication of the bearings to continue and extending the pump’s operating time under these critical conditions.

As zirconium oxide is non-metallic, the isolation shell also avoids the eddy current losses associated with metallic isolation shells, offering the potential for additional energy savings.

Reducing the Risk of Magnetic Drive Pump Failure

Dry running should always be avoided wherever possible, but in real-world pumping applications, unexpected operating conditions can occur. Diamond-coated RunSafe SSiC bushes provide CDR magnetic drive pumps with an additional layer of protection in these circumstances.

As the dry-running tests demonstrate, RunSafe SSiC bushes with aDLC coating can enable a magnetic drive pump to withstand an extended period of operation under these conditions before failure occurs.

The benefits also extend to normal pump operation. Reduced friction can contribute to lower power consumption and reduced wear, supporting the overall efficiency, reliability and service life of the pump.

To find out more about our magnetic drive centrifugal pumps and their dry-running protection, contact the CDR Pumps team on 01933 674777 or email sales@www.cdrpumps.co.uk