A pump is a device that moves a gas or liquid from one area to another. This can be done by accelerating the liquid using centrifugal forces (centrifugal/rotodynamic pumps) or by grabbing a certain amount of liquid and physically pushing it towards where it needs to go (positive displacement pumps).

Pumps are perhaps the most widely used mechanical devices and their designs vary as much as their applications. They are used in domestic applications for washing machines, in municipalities for sewage and water treatment management, in HVAC systems to control condensation collection, in industrial steam systems to return cooled water to the boiler (boiler feed pump), for irrigation, flood control, and even pumping water out of your sinking ship. Some types of pumps are:

Centrifugal Pumps

Centrifugal pumps use a spinning propeller to increase the velocity of the liquid. The propeller spins inside a chamber that has a larger volume than the outgoing pipes so that when the water, which is at an increased velocity, enters the outgoing pipe it is funneled down, and thus compressed. These pumps are generally classified as horizontal (picture above) or vertical (picture at top of page). Another common classification/ nomenclature for these pumps is single stage versus multi-stage. The pump above is a single stage pump because the water meets one impeller and then is ejected. In a multistage pump, the water pressure will be increased by one impeller and is then fed to another impeller to increase the pressure even more.

Centrifugal Pump Monitoring Options

440 Switch with External Sensor (Above)
Provides local contacts as well as 4-20mA output for interface with PLC. Sensor is located on pump while 440 switch is located in a more electronic friendly environment.

SA6200 and 5535
Provides 4-20mA output for interface with a PLC / DCS. Dynamic signal is available from front panel for vibration analysis purposes. Provides options for custom filters, local display/indication, or galvanic isolation.

ST5484E / ST5491E
The ST5484E provides for the simplest installation available. Since it’s a loop-powered device, only two wires are needed for full operation. The ST5484E is connected directly to a PLC / DCS. Optional filtering and dynamic outputs are available. The ST5491E has a local indicator.

Special Case - Large Vertical Pumps

Large pump applications, such as the one shown above, require a more thorough monitoring scheme than smaller applications. For example, while it may be beneficial to monitor bearing temperatures of smaller pumps, it is a necessity for larger applications.

The Metrix solution provides a vibration sensor for all bearings, an impact sensor to detect cavitations, and a DATAWATCH monitor. The DATAWATCH monitors all vibration and temperature readings (including bearing RTDs and Motor Winding Temperatures [provided by others]) and compares them to pre-programmed setpoints in order to change the state of Alarm and Danger relay outputs.

The DATAWATCH also provides trending of all signals, audit tracking, Ethernet and RS232/485 communications (Modbus/TCP), removable memory storage, USB ports, and a color touch screen interface. Metrix can also provide junction boxes for wiring convenience as well as DATAWATCH enclosures that are environmentally rated and have all inputs and outputs pre-wired to rear panel mounted terminal blocks.

Special Case - Pumps with Journal Bearings

Some pumps, especially pumps that run at high speeds and / or high loads, use journal bearings as opposed to rolling element bearings. Journal bearings use a layer of oil to isolate the shaft from the bearing. Therefore, the shaft is actually floating on a cushion of oil and has no contact with any other metal. Because of the oil layer, a vibration signal produced by the shaft does not have a path to travel to the machine casing. That means that a seismic sensor placed on the case of the pump cannot properly sense what is going on with the shaft.

This makes it necessary to use proximity sensors to detect shaft faults. A proximity probe mounts through the case of the machine and senses the position of the shaft relative to the probe tip. The pump casing holds the probe steady so that any movement in the shaft will cause the proximity probe / transmitter to give an indication. This type of measurement is termed “relative” because the shaft movement is being measured in relation to the machine casing.

Positive Displacement Pumps

Positive Displacement pumps handle liquids or gases in a much more direct manner. These pumps use one of several methods to physically grab a quantity of liquid and push it to where it needs to go. A reciprocating pump operates in much the same way as a reciprocating compressor in that it uses a chamber filled with liquid (or gas) which is compressed by a moving cylinder before the liquid is released into the delivery system (piping). Gear pumps, vane pumps, helical pumps, and Peristaltic pumps all use interlocking / rotating parts between which liquid is trapped between and then pushed out of.

Generally speaking, positive displacement pumps are too small to cause damaging vibration or are so inexpensive that a vibration monitoring system is un-economical. That’s not to say that a situation will never come up in which a positive displacement pump needs to be monitored for vibration. In this case, please consult the Metrix factory for monitoring options.