====== Vessel Pumps ======

Cargo pumps are placed at the bottom of a ship because the height that a pump can push a liquid is limited only by the power of the pump.[(:ref:tanker_chartering)]

A tanker uses its own pumps for discharging cargo and loading and discharging ballast, while cargo loading is carried out using shore pumps.[(:ref:tanker_chartering)]

===== Centrifugal Pump =====

In the largest ships, the most common form of pump is the centriíugal type, vvhich is capable of a high discharge rate and may be driven by steam, diesel or electric power.[(:ref:tanker_chartering)]

The centrifugai pump is limited in the range of Products it can easily handle. It does not handle highly viscous iiquids very eífficiently but, given the advent of doubie-hull vessels, this has allowed the creation of suction wells in modern vessels, and on its own at reduced speed, it is able to take the tanks to almost empty, particularly when fitted with a form of Vac-Strip system.[(:ref:tanker_chartering)]

Ships fitted with centrifugal pumps also require stripping pumps. As mentioned above, a
centrifugal pump cannot remove the last metre of cargo from the tank, being effectively a
turbine that tends to draw in air. The stripping pump is normally a small-capacity reciprocating pump, which is able to handle the small quantities of cargo at the bottom of the tank.[(:ref:tanker_chartering)]

===== Reciprocating Pump =====

This type of double-acting pump has a steam-driven piston and pumps liquid at each stroke. It is driven by saturated steam - a relatively low-temperature steam and water mix - because the steam has to lubricate the pump. Although it is <wrap hi>not particularly powerful</wrap>, it <wrap hi>can handle a wide range of Products</wrap> and can keep pumping so long as liquid flows into the chambers.The reciprocating pump is very reliable but has a rather <wrap hi>low discharge rate</wrap>, so is generally <wrap hi>limited to smaller tankers</wrap>.[(:ref:tanker_chartering)]

===== Positive Displacement Pump =====

Positive displacement pumps add energy to a fluid by applying force to the liquid with a mechanical device such as a piston or plunger. A positive displacement pump decreases the volume containing the liquid until the resulting liquid pressure equals the pressure in the discharge system.

https://www.sciencedirect.com/topics/engineering/positive-displacement-pumps

==== Screw Pump ====

This type of <wrap hi>low-capacity, positive displacement pump</wrap> can handle a wide range of liquids and is <wrap hi>most commonly found on chemical and vegetable oil tankers</wrap>. It uses the action of two gears in mesh to drive the liquid.[(:ref:tanker_chartering)]

===== Deepwell Pump =====

Found on chemical and gas tankers and also some modern product carriers, a deepweil pump
is situated in the bottom of each tank and thus eliminates the need for a pump room and
avoids the problems inherent in trying to suck out a tank from deck level. Normally hydraulically
powered, the deepwell pump is useful where a high level of segregation is required. In chemical
tankers and clean product tankers, where segregation is important, each tank vvill have its own
pump and line, and otten its own maniíold, perhaps shared with its corresponding tank on the
other side.[(:ref:tanker_chartering)]

===== Stripping Pumps =====


Because larger cargo pumps are not suitable for draining the last liquid from
a cargo tank, the ship is íìtted with small pumps known as stripping pumps.[(:ref:tanker_chartering)]

These are much smaller than the main cargo lines because they handle relatively small quantities of oil and pumping rates are slower. [(:ref:tanker_chartering)]

===== Pump Room =====

There is a danger that gas can escape from the seals on the pump shafts, so the pump room is kept separate from the rest of the ship and is usually situated foPA^ard of the engine room and aft of the cargo tanks.[(:ref:tanker_chartering)]