Standard submerged pumps whose slide bearings are flushed by the pumping liquid or other media often generate difficulties for the operator. They are not safe to run dry. Dry-running damage to the slide bearings can also occur if gas fractions or solids get into the pump, or accumulate in the bearing area during standstill. In practice, such hydraulic malfunctions regularly cause severe damage, and this can become particularly dangerous in the case of explosive substances or hazardous combinations of pumping media, which are frequently found in the chemical and petrochemical industries.
The submerged column pumps from Bungartz are designed specifically for these or other such difficult pumping tasks. All pumps from this manufacturer have a hydrodynamic seal, which prevents the secondary sealing (e. g. packed gland, double mechanical seal, magnetic drive etc.) from coming into direct contact with the pumping medium. One advantage here are the grease-lubricated rolling bearings, which are not in contact with the product and are lubricated for life. A rolling bearing service life of more than five years of continuous operation is the norm here. Instead of relying on sensitive mechanical seals as the primary seal, Bungartz, as a manufacturer of special centrifugal pumps, likewise works with various concepts in its submerged column pumps.
Importance of the immersion depth
The immersion depth of a pump (e.g. the T, T-AN or F-T pumps, all three of which have a cantilever shaft design) is dimensioned on a requirement-specific basis. The guiding factor for pumps with a cantilever shaft design may be the deflection of the shaft under operating conditions. The critical speed is also significant. This is the speed at which the natural frequency of vibration of the shaft coincides with the shaft speed. This frequency has at least 20 % margin of safety relative to the desired operating speed. The shaft length of submerged column pumps with a cantilever shaft design can reach up to 1.5 m, measured from the lower rolling bearing to the impeller. This is dependent on the speed. Depending on the fluid level, the area of the bearing bracket can be used. In addition, the suction pipe extension can be used for deeper suction.
Depending on the requirements, the T-AN, for example, can be used as a self-regulating pump in the pit area – without shaft seal and with an overflow opening for back-pressure relieving. This pump is also in use as an external pump (add-on) with a support pipe as an overflow connection. It is also suitable for installation in a container, in which case an additional pipe is added for pressure compensation. In installations of this type of pump, the bearing is never located in the pumping liquid – not even in pumps with shaft bearing below the liquid level in the container surrounding the pump. And they share more common features with other pump types from the manufacturer: low operating and maintenance costs.
Specialist for toxic media
This also applies to the specialist in the submerged column pump range, the MPCT-AN. It is approved for hazardous and toxic media, and even for Atex zone 0. Its pump hydraulics– specifically the pump casing and impeller – are indeed submerged in the pumping liquid at startup. However, in contract to submerged motor pumps, the drive motor is located above the dome of the container. On the one hand, and like the other pumps from this manufacturer, the safety concept is based on the total hydrodynamic seal by means
of impeller back vanes. On the other hand, gas barriers (sealing gas) protect the bearing unit against penetration by product vapours. The bearings and sealing unit run without product contact, and are thus dry at all times. The dry-running vortex-free magnetic drive (through a ceramic containment can) has no contact with the pumping liquid or its gases. The pump is likewise hermetically sealed.
The vertical design of the pump is also an advantage. The design itself thus prevents the seal and the lifetime-lubricated bearing from coming into contact with the pumping medium, even at a standstill. As with
all pumps in the V-AN series, the self-regulating behaviour of this pump ensures adaptation to changing feed rates. This
type of pump does not use suction, but automatically regulates its speed to the
feed flow of medium. Fluctuating feed rates, sporadic use, and in particular the total emptying of tanker trucks and tank wagons are therefore amongst their specialities.
Everyday pumping application
A light oil processing plant produces waste water containing hydrocarbons. The slop medium – waste water and hot liquid hydrocarbons – is collected in separate containers. The liquid fraction is collected in a single tank. At long intervals, the submerged column pump installed in the container intermittently pumps the material collected in the container to a disposal facility. Thanks to the two-part shaft seal system of the pump, consisting of a magnetic drive to hermetically seal out the atmosphere and a mechanical seal to protect the pump shaft‘s rolling bearings against the ingress of the liquid from the container, the pumping process is safe at all times. The pump has been running trouble-free for years.
Special tasks like this and others are what has gained this company its reputation as a problem-solver. The engineers and their colleagues at the pump manufacturer provide comprehensive advisory services and individual recommendations. They support customers through the entire process, starting from the reliable design of the pump, through to the commissioning process and beyond.
Paul Bungartz GmbH & Co. KG, Düsseldorf