Showing posts with label TECNOLOGY AND KNOWLEDGE. Show all posts
Showing posts with label TECNOLOGY AND KNOWLEDGE. Show all posts
Monday 19 October 2015
Sunday 18 October 2015
ACCUMULATOR
An accumulator is a pressure storage reservoir in which
hydraulic fluid is stored under pressure from an external source. The storage
of fluid under pressure serves several purposes in hydraulic systems.
ACCUMULATOR :The accumulator absorbs the surge pressure that occurs within
the hydraulic circuit, decreases the pulsing of the hydraulic pressure, and
acts as a temporary source of pressure when the hydraulic pumps is shut off.
In some
hydraulic systems it is necessary to maintain the system pressure within a
specific pressure range for long periods of time. It is very difficult to
maintain a closed system without some leakage, either external or internal.
Even a small leak can cause a decrease in pressure. By using an accumulator,
leakage can be compensated for and the system pressure can be maintained within
an acceptable range for long periods of time. Accumulators also compensate for
thermal expansion and contraction of the liquid due to variations in
temperature.
Figure 9-5.–Cross-section view of a piston-type accumulator
with a tailrod.
A liquid, flowing at a high velocity in a pipe will create a
backward surge when stopped suddenly by the closing of a valve. This sudden
stoppage causes instantaneous pressures two to three times the operating
pressure of the system. These pressures, or shocks, produce objectionable noise
and vibrations which can cause considerable damage to piping, fittings, and
components. The incorporation of an accumulator enables such shocks and surges
to be absorbed or cushioned by the entrapped gas, thereby reducing their
effects. The accumulator also dampens pressure surges caused by pulsating
delivery from the pump.
There are times when hydraulic systems require large volumes
of liquid for short periods of time. This is due to either the operation of
large cylinders or the necessity of operating two or more circuits
simultaneously. It is not economical to install a pump of such large capacity
in the system for only intermittent usage, particularly if there is sufficient
time during the working cycle for an accumulator to store up enough liquid to
aid the pump during these peak demands.
The energy stored in accumulators maybe also used to actuate
hydraulically operated units if normal hydraulic system failure occurs. Four
types of accumulators used in Navy hydraulic systems are as follows:
1. Piston type
2. Bag or bladder type
3. Direct-contact gas-to-fluid type
4. Diaphragm type
PISTON-TYPE
ACCUMULATORS
Piston-type
accumulators consist of a cylindrical body called a barrel, closures on each
end called heads, and an internal piston. The piston may be fitted with a
tailrod, which extends through one end of the cylinder (fig. 9-5), or it may
not have a tailrod at all (fig. 9-6). In the latter case, it is referred to as
a floating piston. Hydraulic fluid is pumped into one end of the cylinder and
the piston is forced toward the opposite end of the cylinder against a captive:
Figure 9-6.—Floating piston-type accumulator.
charge of air or an inert gas such as nitrogen. Sometimes the
amount of air charge is limited to the volume within the accumulator; other
installations may use separate air flasks which are piped to the air side of
the accumulator. Piston accumulators may be mounted in any position. The gas
portion of the accumulator may be located on either side of the piston. For
example, in submarine hydraulic systems with tailrod pistons, the gas is
usually on the bottom and the fluid on top; in surface ships with floating
pistons, the gas is usually on the top. The orientation of the accumulator and
the type of accumulator are based upon such criteria as available space,
maintenance accessibility, size, need for external monitoring of the piston’s
location (tailrod indication), contamination tolerance, seal life, and safety.
The purpose of the piston seals is to keep the fluid and the gas separate.
Usually, tailrod accumulators use two piston seals, one for
the air side and one for the oil side, with the space between them vented to
the atmosphere through a hole drilled the length of the tailrod. When the
piston seals fail in this type of accumulator, air or oil leakage is apparent.
However, seal failure in floating piston or nonvented tailrod accumulators will
not be as obvious. Therefore, more frequent attention to venting or draining
the air side is necessary. An indication of worn and leaking seals can be
detected by the presence of significant amounts of oil in the air side.
BLADDER-TYPE
ACCUMULATORS
Bladder- or bag-type accumulators consist of a shell or case
with a flexible bladder inside the shell. See figure 9-7. The bladder is larger
in diameter at the top (near the air valve) and gradually tapers to a smaller
diameter at the bottom. The synthetic rubber is thinner at the top of the
bladder than at the bottom. The operation of the accumulator is based on
Barlow’s formula for hoop stress, which states: "The stress in a circle is
directly proportional to its diameter and wall thickness." This means that
for a certain thickness, a large diameter circle will stretch faster than a
small diameter circle; or for a certain diameter, a thin wall hoop will stretch
faster than a thick wall hoop. Thus, the bladder will stretch around the top at
its largest diameter and thinnest wall thickness, and then will gradually
stretch downward and push itself outward against the walls of the shell. As a
result, the bladder is capable of squeezing out all the liquid from.
Figure 9-7.—Bladder-type accumulator.
the accumulator. Consequently, the bladder accumulator has a
very high volumetric efficiency. In other words, this type of accumulator is
capable of supplying a large percentage of the stored fluid to do work. The
bladder is precharged with air or inert gas to a specified pressure. Fluid is
then forced into the area around the bladder, further compressing the gas in
the bladder. This type of accumulator has the advantage that as long as the
bladder is intact there is no exposure of fluid to the gas charge and therefore
less danger of an explosion.
DIRECT CONTACT
GAS TO FLUID ACCUMULATORS
Direct-contact gas-to-fluid accumulators generally are used
in very large installations where it would be very expensive to require a
piston-or bladder-type accumulator. This type of accumulator consists of a
fully enclosed cylinder, mounted in a vertical position, containing a liquid
port on the bottom and a pneumatic charging port at the top (fig. 9-8). This
type of accumulator is used in some airplane elevator hydraulic systems where
several thousand gallons of fluid are needed to supplement the output of the
hydraulic pumps for raising the elevator platform. The direct contact between
the air or gas and the hydraulic fluid tends to entrain excessive amounts of
gas in the fluid. For this reason, direct contact accumulators are generally
not used for pressures over 1200 psi. The use of this type of accumulator with
flammable fluid is dangerous because there is a possibility of explosion if any
oxygen is present in the gas, and pressure surges generate excessive heat. For
this reason, safety fluids are used in this type of installation.
DIAPHRAGM ACCUMULATORS
The diaphragm-type accumulator is constructed in two halves
which are either screwed or bolted together. A synthetic rubber diaphragm is
installed between both halves, making two chambers. Two threaded openings exist
in the assembled component. The opening at the top, as shown in figure 9-9,
contains a screen disc which prevents the diaphragm from extruding through the
threaded opening when system pressure is depleted, thus rupturing the
diaphragm. On some designs the screen is replaced by a button-type protector
fastened to center.
Figure
9-8.—Direct-contact gas-to-fluid accumulator.
Figure 9-9.—Diaphragm accumulator.
of the diaphragm. An air valve for pressurizing the
accumulator is located in the gas chamber end of the sphere, and the liquid
port to the hydraulic system is located on the opposite end of the sphere. This
accumulator operates in a manner similar to that of the bladder-type
accumulator.
Saturday 17 October 2015
Sunday 11 October 2015
Sunday 4 October 2015
2 SPR sniper rifle made by PT Pindad, defense equipment company owned by the Government of Indonesia, the center became a byword in the international world. Apparently, advanced sniper rifle used Kopassus can not be made by any country.
So what's so special? Well, the following facts Pindad arms to Kopassus that gegerkan world, as compiled Merdeka.com: Check the following pages other advantages of SPR Rifle 2 has reached the target range of 2 km. But the effective distance of 1 km.According to the Head of the Department of Communication PINDAD, Sena Maulana, little foreign-made sniper that can compete with the SPR 2.
Most foreign-made sniper target range under SPR 2.
"The sniper Rival black arrow and truvellow. Both are under the gun Kopassus SPR 2 of this scope," he said. (Ism
SPR rifle ammunition 2 also has a somewhat special, can give three effects simultaneously. Pierce, burn and explode inside the target at a time
2 SPR sniper rifle relatively large class. SPR 2 has a 12.7-millimeter caliber ammunition. In the market usually just 5.62 millimeters not comparable with Kopassus weapons ini.jenis SPR sniper rifle bullet 2 PT Pindad feared many countries. This bullet can penetrate armored vehicles though. "Ammunition of 12.7 mm anti-material. Bullet type most feared because it can penetrate tanks and armored vehicles," said Head of the Department of Communication PINDAD, Sena Maulana.
2 SPR sniper rifle originated from sniper SPR 2 foreign-owned military did not dare tested. Then PINDAD trying to test and ultimately make their own. "In 2003, TNI has 3 shoots of other countries but do not dare to test for heavy and bulky. Finally we test together and our own in 2006, the inception of this Special Forces weapon," he said.
PT Pindad produces SPR sniper rifle 2 for use Kopassus. This weapon also invite admiration of the world. "We're making 150 shoots (SPR rifle 2) for Kopassus. World sniper has direct international uproar, how about more?" said Head of the Department of Communication PINDAD, Sena Maulana.
According to him, the ability to make weapons PINDAD it makes some countries attracted want to have. Currently arms exhibition in 2014 (Indo Defence) this time many countries who want to see up close the rifle. "The foreigners are also directly see here. They've heard the greatness of this Special Forces weapons, we are able to make," he said.
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