Api 676 latest edition

Twin screw rotary process pumps designed and manufactured according to API 676 lasted edition for a compact design and generously sized components make these pumps suitable for the most critical applications.
2V-M pumps can be manufactured in all the materials combination class and in special alloys for chemically aggressive services.

Non lubricating low and medium viscosity, corrosive and dangerous fluids,

Flammable and Heavy Liquids, Petroleum Distribution, Petrochemical Processing, Petroleum Production and Refining, Offshore, Hydrocarbon Processing, High Temperature Service

Miscellaneous Services, Catalytic Cracking, Heavy Oil and Upgrading, Crude Handling and Treatment,

Pump description

1) Suction and discharge connections according to ANSI. IN Line or SIDE TOP disposition, other standards like UNI, DIN or BS available.

2) Casted or welded pump casing available. Pump gasket seals is a fully confined, spiral wound metal or O-ring gaskets. Possibility to install heating jacket chamber steam or high temperature thermal oil.

3) Renevable pump casing insert (liner) inset into the pump casing positively locked. Different metallurgies and material combinations are available.

4) Internal or external bearing housing installation is available in function of desired solution to ensure high pump reability.
They are made in one piece and has machined pilot fit to pump cover. Both radial and thrust bearing are sized to give 25.000 Hours minimum Lh-10 rating life with continuous operation at rated pump conditions. Bearing housings are designed to remove the mechanical seals without removing bearings. Bearing are flood oil lubricated. Oil level is maintained by a constant level oiler. The oil chamber is sealed with non-contact labyrinth deflectors as API 676 requirements, up to IP66 mechanical protection. Water jacketed bearing housing’s are available also with OIL Mist lubrication connections.

5) Pump casing available in both horizontal and vertical disposition. Suction and discharge flanges can be in Line or SIDE Suction and TOP discharge flange in function of plant necessities.

6) Different screw profiles in function of desired performances up to multiphase design, single or multiple screws turns to allow high pressure or high vacuum capabilities.
7) Pump covers, are aligned by machined pilot fit.

8) MECHANICAL SEAL CHAMBER is simple or according to API standard.
Single, double, balanced or unbalanced mechanical seal, with all possible combination flash and quench glands are available up to latest API 682 mechanical seals configuration.

9) Water or Air cooled bearing housings, by means of fin-tubes exchangers.

10) Several heating jacket solutions are available, suitable for steam vapour or hot oil, foot or entire double casing configurations.

11) Built in or separate PLV (pressure limit safety valve) are available as option.

Working principle

The pump is timed twin screw rotary type and it is composed by a couple of screw rotors, with opponent coils and mutual special outline that work inside a chamber set in the pump casing.
On every rotor, two contrasted and synchronized screws are realized to balance every hydraulics thrust, and through external timing device. The gear couple with the rotors are synchronized together.
The pumped up fluid goes into the pump casing from the aspiration flange and then divided in two different parts, after it is aspired by the screws and pushed in axial way toward the delivery flange.
The special opposed screws profile create during the chambers rotations which constantly push without beats toward the delivery pump, in this way, the pump is able to transport every kind of fluid independently from the fluid viscosity.
The synchronism device, timing gears, prevents any metallic contact during rotation and enable the pumping of non-lubricating fluids as well as aggressive media. This design also allows dry running and self-priming capability.
The design yields to have always fluids inside of the pump casing and allow the pump can be auto primed without adding peculiar external devices.

Twin screws pumps (PD pumps) create flow, centrifugal pumps create pressure. In a PD pump, flow is created by enclosing a volume at suction, moving it to discharge, and releasing it. Pressure is created by the system’s response to flow.
If delivery pressure is lower than rated, the flow would exit without any problem for the pump..
Centrifugal pumps create pressure by first imparting velocity to the fluid with the impeller, then converting the velocity to pressure with the volute.
The centrifugal pump cannot be work at lower pressure than rated, and If there was no discharge flange connection, noise and vibrations starting and centrifugal pump shall be broken quickly.
If the viscosity increase, the centrifugal pumps reduce its performance (loss of delivery pressure and capacity) and increase a absorbed power.
In a PD pump delivery pressure is independent from the viscosity and, when viscosity increase, the pump performance reaming the same or the flow increase.

The PD pumps is the most option when the fluid viscosity change in the process.