Oil pressure

As reservoir pressure is reduced by oil production, additional recovery mechanisms may operate. One such mechanism is natural water drive. Water from an adjacent more highly pressured formation is forced into the oil-bearing formation by the pressure differential between the formations. Another mechanism is gas drive. Expansion of a gas cap above the oil as oil pressure declines can also drive additional oil to the wellbore. Produced gas may be reinjected to maintain gas cap pressure as is done on the Alaskan North Slope. Additional oil may also be produced by compaction of the reservoir rock as oil production reduces reservoir pressure. 

An iajection mol ding machine is operated by hydrauHc power and equipped with an electric motor and hydrauHc pump. The maximum hydrauHc oil pressure is ca 14 MPa (2000 psi). A hydrauHc cylinder opens and closes the mold and holds the mold closed duriag iajection another cylinder forces the screw forward, thereby injecting the melt iato the mold. A separate hydrauHc motor turns the screw to plasticate, homogenize, and pressurize the melt. Control of these movements is a combined function of the hydrauHc and electrical systems (35—37). 

In operation seal oil pressure is about 30-50 psi over the process gas pressure. The high-pressure oil enters the top and completely fills the seal cavity. A small percentage is forced across the carbon ring seal faces. The rotative speed of the carbon ring can be anywhere between zero and full rotational speed. Oil crossing the seal faces contacts the process gas and therefore contaminated oil. The contaminated oil... 

FIG. 29-66 Oil-film hearing with oil pressure created preload (pressure dam desi nj. 

An interlock is provided through a centrifugal type of pressure switch (PS) to trip the engine in the case of low lube (lubricating) oil pressure during a run. Since during a. start oil pre.s.sure has not built up, a timer, 7 j is introduced to bypass the trip interlock and avoid a false trip. A relay (contactor), d], is used to provide lube oil pressure interlock. 

Thrust loads on die bearings Seal gas pressure and flow Lube oil pressure... 

A bladder or diaphragm-type aeeumulator should be supplied to provide proper lube oil supply to the bearings during expander-eompressor eoast-down in the event lube oil pressure is lost. The aeeumulator must be fitted with a preload filling system and neeessary bleed and bloek valves. 

Lube oil pressure is generally eontrolled by a self-eontained pressureregulating valve that automatieally maintains a eonstant lube oil pressure aeross the bearings. The valve is normally adjustable, but is usually preset at the faetory. The valve flow eapaeity must be suffieient to bypass exeessive flow if both main and standby pumps are operating simultaneously. 

Before mining on tlie seal gas and lube oil pumps, initiate power to the eontrol panel to eonfirm tlie indieator lights are funetioning. At tliis time, there is no seal gas or lube oil pressure so tlie low lube oil alarm, low lube oil pressure shutdown, and seal gas alarm light should be on. 

After the lube oil pumps have been running for approximaely 15 min, elose the pump and filter bypass and slowly pressurize the system to establish normal lube oil pressure. The alarm and shutdown lights should turn off by pushing the reset button on the annuneiator panel. 

Mechanical seals vapor recovery sealing glands by oil pressure maintenance Vapor incineration Inspection and maintenance... 

Demonstrate the oil pressure control valve can control oil pressure. 

In operation, seal oil pressure is held at a differential of 35-50 psid (2.4-3.5 bar) over the proeess gas pressure whieh the seal is sealing against. This high-pressure oil ean be seen entering in the top in Figure 13-30 and... 

The majority of the oil flows out of the uncontaminated seal oil drain after taking a pressure drop from design seal oil pressure to atmospheric pressure across the breakdown bushing. An orifice is placed in parallel with the breakdown bushing to meter the proper amount of oil flow for cooling. The contaminated oil leaves through the drain to a degasifier for purification. 

When possible, gears should be run-in on initial startup. Speeds and loads should be inereased in pereentage inerements. Lube oil temperature, and pressure and bearing temperatures should be observed and adjustments made to the lube system as required. The number of adjustments made will depend on the eomplexity of the system. Oil pressure is of primary importanee. When an auxiliary pump has been provided, oil should be eireulated before the aetual start. If not, the pump should be primed, and the journals wetted with oil. Primer holes are sometimes provided or alternate journals ean be oiled through the holes provided for bearing temperature deteetors. 

Low oil pressure switehes are provided on the pumps and diseharge header ahead of the eoolers and filters, sometimes after the eooler and filters, and always at the end of the line where the redueed oil pressure feeds the various users. A signal from any of these should start the motor-driven pump and all alarms should be aetivated in the eontrol room. The emergeney oil pump ean be driven with an AC motor but from a power souree that is different to the standby pump. When de power is available, DC eleetrie motors ean also be used. Proeess gas or air-driven turbines and quiek-start steam turbines are often used to drive the emergeney pumps. 

The system should have an aeeumulator to maintain suffieient oil pressure while the standby pump aeeelerates from an idle eondition. An aeeumulator beeomes a must if a steam turbine drives the standby pump. Overhead tanks are speeified by many users to assure flow to eritieal maehinery eomponents. The sizing of the tanks varies depending on the applieation. In some gas turbine applieations, the bearings reaeh maximum temperature as long as 20 minutes after shutdown. 

To ensure the required eonstant pressure, a loeal pressure eontrol loop is provided on eaeh system—turbine lube oil, eompressor lube oil, and eontrol oil. Eaeh oil pressure system should be reeorded in the eontrol room to provide troubleshooting information. The sueeess of the oil system depends upon not only the instrumentation, but upon proper instrument loeation. 

The minimum alarms and trips reeommended for eaeh major driver and driven maehine should be a low oil pressure alarm, a low oil pressure trip (at some point lower than the alarm point), a low oil level alarm (reservoir), a high oil filter differential pressure alarm, a high bearing metal temperature alarm, and a metal ehip deteetor. See Table 15-1. 

Momentary loss of oil pressure. Sometimes eneountered while switeh-ing filters or eoolers. 

COMPRESSOR WILL NOT START 1. Power supply failure. 2. Switchgear or starting panel. 3. Low oil pressure shut down switch. 4. Controi panel. NOISE IN CYLINDER 1. Loose piston. 2. Piston hitting outer head or frame end of cylinder. 3. Loose crosshead lock nut. 

FRAME KNOCKS 1. Loose crosshead pin, pin caps or crosshead shoes. 2. Loose/worn main, crankpin or crosshead bearings. 3. Low oil pressure. 4. Cold oil. 5. Incorrect oil. 6. Knock is actually from cylinder end. 

LOW LUBE OIL 1. Faulty lube oil pressure gauge or switch. Note 2. Loose or broken bolting. 

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