General Description. Top cover plate. Pipe stack. Pump unit.
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I recently met a 3rd officer. Few seconds later when I got my breath back, I realised how Framo has captured the tanker market. This makes the knowledge of Submersible pumps and Framo system so much important. Framo submersible pumps are centrifugal pumps. So before we discuss Framo pumps, we must know how a centrifugal pump works? I am not going in details of how a centrifugal pump works. But if you watch the above video, you would know that it has three main components.
Prime mover provides the energy for the impeller to rotate. Impeller rotates and pushes the liquid into the volute casing. Volute casing has a spiral structure. It has narrow opening at the entry of liquid and the size of opening increases along the passage of liquid. This means that as the liquid travels in the volute casing, velocity reduces and pressure increases.
This is the most basic points we should know before we proceed with any kind of centrifugal pump. For the centrifugal pump to work, impeller need to rotate. But impeller would not rotate on its own. It need a source of energy prime mover. In steam turbine centrifugal pumps, this energy is provided by steam. In Framo system, you will not be able to see the hydraulic motor as it is placed in the outer casing.
It is important that hydraulic oil tank always have sufficient oil for the high pressure pump. If it has less or no oil, the pump will get damaged. If the suction valve for the high pressure pump is closed, the power pack will trip.
This ensures that the suction valve of the pump to take suction from hydraulic tank is not inadvertantly closed. There is a sensor arrangement for the suction valve, which senses if the suction valve is fully open. In old Framo system this could be a manual valve with its handle touching the sensor. If the suction valve is even slightly closed, its looses the touch of sensor and trip is activated. In new systems, the valve is not a manual valves.
In this case the a proximity sensor is fitted on top of the valve, that senses if the valve is fully open or not. For this reason when the oil level in the hydraulic tank goes below minimum level, the power pack will trip. The oil level in the hydraulic tank is kept just above the alarm level. This ensures that any leakage in the line will be immediately detected without the loss of much of hydrualic oil.
If the low oil level trip is activated, the reason for low level must be investigated. The oil can then be refilled either from the standby tank or spare drums whichever available.
This pump is inside the cargo tank and there are two liquids hydraulic oil and cargo that should not come in contact. If the hydraulic oil leak into the cargo, cargo can damage. If cargo goes into the hydraulic oil, the hydraulic system will damage. As you might have guessed, there is something in the Framo pump to prevent that. There is hydraulic seal that prevents hydraulic oil leakage to the cargo side.
And there is cargo seal that prevents cargo leaking into the hydraulic side. You can think of cofferdam as a steel cup with cargo seal at the bottom. Any hydraulic oil or cargo leakage will collect in this cofferdam.
It is important to know if the cofferdam is empty or not. And this is done by purging the cofferdam. If any of the seal is leaking, it need to be replaced with new seal after the discharging and tank cleaning of the tank. Framo has a purging routine which shows when the purging of the pump cofferdam need to be carried out.
For some cargoes, we are supposed to not do the cofferdam purging. These may be toxic cargoes such Toluene Diisocynate or solidifying cargoes such as Palm oil. In these cases we need to fill the cofferdam with some liquid DOP in case of loading TDI so that cofferdam is not blocked with the cargo. To achieve this, we should be able to control the flow of the hydraulic oil to the hydraulic motor of the Framo pump.
This is because more the flow of pressurised oil to the hydraulic motor, more speed the impeller will rotate. This is exactly what Speed torque controller does. STC is fitted on top plate of the pump on main deck. The Hydraulic oil inlet pass through the STC. STC of the pump controls the speed of the pump by allowing only the required amount of hydraulic oil to pass through to the hydraulic motor. STC also prevent the pump to overspeed by controlling the amount of oil to the hydraulic motor of the pump.
With local control valve, we can control the speed of the pump locally from the pump itself. This becomes handy during stripping of the tanks or tank cleaning. When we close the knob by turning clockwise , the STC passes the oil to the pump. When we open the knob by turning anti clockwise , the STC bypasses all the oil and nothing goes into the hydraulic motor.
Pump stops or do not run in this case. We do this by a lever provided in the cargo control room. Each pump has a lever that connects with the STC of that pump by a hydraulic control line.
As we push the lever up to start the pump, a signal in form of hydraulic control line pressure goes to the STC. STC then releases the amount of oil to the hydraulic motor which will be corresponding to the amount to lever lifted.
If the local control knob is in open position, the pump will not work even when the pump lever is operated from CCR. For the Framo system to work efficiently, the hydraulic oil used in the system need to be in absolute good condition. Feed pump always keep on running, days in a year, 24 hours a day. Feed pump maintains positive pressure in the lines and hydraulic system. It continuously recirculate the oil through entire hydraulic oil system.
Usually pressure of more than 5 Bars is maintained in the system even when the system is not in use. Now when the system is always under positive pressure, the chances of moisture ingress are minimum. Air if any is auto released to the Hydraulic tank while recirculation. Off course if air is still suspected in the system, there is air purging arrangements in the Framo. And any particles in the system are filtered while feed pump runs the hydraulic oil in recirculation mode. This is because the recirculated oil is made to pass through the filter.
Recirculation of hydraulic oil through feed pump also avoids oil temperature variations at different parts of the hydraulic system. It helps in keeping the feed pressure on the suction side of the main hydraulic pump.
One of the feed pumps must always be running when the power packs are not in operation. When starting the first main power pack, two feed pumps will automatically start before the power pack is started. This is called high capacity mode of feed system. This is to keep the feed pressure on the suction side of the main hydraulic pump.
In this case the third feed pump will start automatically. Hydraulic oil used in any hydraulic system has a optimum temperature range for use. This is because higher temperature can damage the seals and other components and also it accelerates the degradation of oil. Depending upon the surrounding temperature, the hydraulic oil used in Framo may be below or above this temperature range. If it is above the optimum range, the oil will need cooling.
If it is below the optimum range, it would need heating. If the surrounding temperature is below 20 C, we need to open the heating and venting valve for heating with one power pack running.
When the oil temperature is well within operating range, other power packs can be started. Same goes for when the surrounding temperature is higher. The hydraulic oil is made to pass through a oil cooler to cool the oil before delivery on deck. The cooling water inlet valve is automatically controlled. It will open at hydraulic oil temperature above 50 C and will close when temperature decreases to below 30 C.
These are the push buttons installed at different locations. When pressed, the hydraulic system will trip immidiately. On each ship, there could be few locations for emergency stop for Hydraulic system. We must know all of these locations. Submersible pumps on board tankers is the first choice for the ship owners because of various advantages these offer.
Framo is leader among the submersible pumps fitted on board tankers. For anyone working on tankers, this makes the thorough knowledge of the Framo system a necessity.
Framo Operation Manual