How centrifugal pumps can be made more reliable….?

Marine-Horizontal-Centrifugal-Pump

If you want to go purchase or investment in a centrifugal pump, you would expect it to trouble free functioning and maintain long time duration. Applying necessary improvements in varied areas such efficiency, reliability and containment helps in making these units more reliable. In addition to this, there are refinements comprising of remote telemetry evaluation, modern pump controls, with mechanical seal/Gland packing designs and variable speed drives. When these improvements are rightly followed, it generates potential for the reliable functioning.

However, this can only be achieved by following 3 basic steps right selection, installation and maintenance.

1.Selection of Pump: Seals, operating conditions and bearings are some of the key elements that prove beneficial in the selection of the pumps. It is imperative that centrifugal pumps should function at or near the set head (In meter) & flow rate (In m3/hour). The bearings of the pump is responsible for holding the rotating parts in their apt position and sized to bear the thrust and radial loads which is produced by the impeller.

There is one design that makes use of disks with or without radial vanes that help in the creation of frictional energy for the displacement of the fluid. Pressure gets balanced amid the disks and the bearings get to bear minimum load.

2.Installation: There are two main elements when it comes to the installation of centrifugal pumps (Both Alignment & Foundation). It has to be ensured that the anchor bolts are set in the concrete foundation in the correct fashion. The base of the foundation has to be chipped in order to permit the grout to follow. Base plates should be very clean, placed in its ideal place and should be leveled prior to the pouring of the grout.

Grout is responsible for bonding the base plate with the foundation and assists in the transmission of moments generated via driver, piping and pump to the foundation. Ensure that the weight of the foundation is three times the pump, pump and the coupling.

  1. Maintenance: A log on pump functioning can prove beneficial in identifying probable critical issues. A log like this comprise of changes in the lubrication, operation durations, maintenance procedures and packing alterations. It will prove beneficial for the periodic readings of flow, power input, suction and discharge pressure, noise levels, bearing temperature and fluid.

Wear rings offer right amount of prevention for the high pressured fluid to get leaked internally. In addition to this, it also offers a mean for minimizing hydraulic thrust of the pump. Because they make a difference in the performance of the pump, elevated clearance can elevate the power requirements by 5-7%.

Why Liquid Pump Seals Fail

Why Liquid Pump Seals Fail

When operating rotating equipment, some end users do not pay enough attention to transient conditions. Startup, slow-roll and standby pump conditions must be evaluated to ensure proper sealing fluid is being supplied to the seals at all times.

Multi spring seal

Startup: The pump is charged, butor near suction pressure. Liquid ethane at the seal faces is slowly leaking and vaporizing. When the pump starts, how long does it take to build the right pressure in the stuffing box and get the pressure above vapor pressure? Additionally, the heat generation between the faces, although not significant, could be enough to increase vapor pressure and vaporize the fluid across the faces. Damage to sealing faces could be a telling sign that this is occurring.

Slow-roll: The same situation as startup but compounded. Without the right speed, the discharge pressure is not generated. The pressure in the stuffing box is not rising quickly enough to ensure the ethane will reach a high enough pressure to overcome the vapor pressure. Also, the heat generation between the contacting faces is increasing, and damage is probably taking place.

Standby: All conditions mentioned above are the same, but the seals are sitting idle for many months without a flush to the seals. During the standby time, evidence has shown that debris has collected at or around the seal faces, which, in turn, adds more complication to the sealing environment.

Inefficient operation: Operating the pump too far outside of the best efficiency range and with the wrong operating parameters results in increased demand for drive power and reduced discharge pressure. Both of these negatively impact the vapor margin in the seal area, which can result in dry running

MECHANICAL SEALS FOR WATER AND WASTEWATER PUMPS

Because mechanical shaft seal failures are the number one cause of pump downtime, the writer decided to dedicate this column to mechanical seal basics.

Years ago, most pump shafts were sealed using rings of soft packing, compressed by a packing gland, but this type of shaft seal required a fair amount of leakage just to lubricate the packing and keep it cool. Then came the development of the “mechanical seal,” which accomplishes the job of restraining product leakage around the pump shaft with two very flat surfaces (one stationary and one rotating).

Main elements of a Mechanical seals

Mechanical seal Info.

Here is mentioned below, there are two seal face :

  • A set of (very flat) machined and lapped primary sealing faces: The very close (near) contact between these two flat mating surfaces, which are perpendicular to the shaft, minimizes leakage. Dissimilar materials are usually used for the faces, one hard and one softer, in order to prevent adhesion of the two faces. One of the faces is usually a non-galling material such as carbon-graphite. The other surface is usually a relatively hard material like silicon-carbide, or ceramic. However, when handling abrasive, two hard surfaces are normally used:
    • One face is held stationary in a housing
    • The other face is fixed to, and rotates with the shaft.
  • A set of secondary static seals, typically O-rings, wedges and/or V-rings.
    • One static seal, seals stationary component(s) to the housing
    • The other seal, seals the rotating component(s) to the shaft (it normally moves axially on the shaft or shaft sleeve)
  • A spring member to maintain face contact, such as a single spring, multiple springs or metal bellows.
  • Other mechanical seal hardware, which includes shaft sleeves, gland rings, collars, compression rings, and/or pins.

Mechanical seals require clean water, or other compatible liquid, for the lubrication of the seal faces. The faces in a typical mechanical seal are lubricated with a boundary layer of gas or liquid between the faces. Lubrication can be provided from the pumped liquid itself or from an external source, depending on system requirements.

seal working info