Ashcroft 1327D - Pressure Gauge Comparator Manual de usuario descargar pdf (Pagina 12)

s affected somewhat by temperature, and by the elastic

istortion of the piston and cylinder when pressure is

eing applied. The effective area of a stainless steel piston

and cylinder increases approximately .068% with a 50

degree F (28 degree C) change in temperature. The

pressure will, therefore be less than indicated at high

temperatures.

.4 Mass, Height, and Buoyancy

The density of air at room temperature and sea level pres-

sure is about 0.0012 grams/c.c., and the mass of the pis-

ton assembly and weights under these conditions will be

reduced by about one part in 7,000 or .014%. When the

submerged part of the piston has a uniform cross section,

as with the 1305D Deadweight Tester, a buoyancy correc-

ion is not necessary. In other designs, the piston is some-

imes enlarged to provide a stop for its upward motion or

for increased strength. If these enlargements are sub-

merged in liquid, a buoyancy correction is necessary.

4.5 Absence of Friction

By rotating the weights and piston, friction effects are

greatly reduced.

4.6 Head of Transmitting Fluid

Oftentimes, the gauge being tested, or the point at which

pressure is being measured, is not at the same level as

the lower end of the piston. A correction, therefore, should

be made for the pressure distance between these points;

the height is considered positive when the gauge is above

the piston. When oil is used in the gauge tester, the cor-

rection will be approximately 0.03 psi (.2 kPa) for each

inch (2.54 cm) difference in level.

4.7 Method of Operation

It is important that the piston be kept floating in mid-posi-

tion, either spinning or oscillating.

4.8 Levelness

The piston assembly should be vertical to within ±1

degree. A 3 degree tilt to piston axis may cause a .13% of

1% error. The deadweight tester is manufactured and test-

ed to 1/10th of 1% accuracy, to this degree of levelness. A

tilt piston/cylinder axis causes excessive friction, due to

side loading of the piston against the cylinder.

4.9 Cleanliness

The weights have been manufactured and tested to a pre-

cision of 0.05%. A buildup of dirt and grease may cause

the weight value to exceed its original tolerance and

produce erroneous pressure readings.

Periodically clean the weights to assure proper

performance.

5.0 MAINTENANCE INSTR

UCTION

5.1 General Maintenance

The Deadweight tester and test pump are designed to

serve as precise pressure measuring standards. They are

precision built units and should be cared for in the same

manner as other sensitiv

e laborator

y equipment. General

maintenance is limited to cleaning and replacement of O-

ring packings, which can be done with tools supplied with

the equipment and requires only limited disassemb

ly of

the gauge tester.

The piston suppor

ting the w

eight platf

orm has been manu-

factured to very close tolerances. It has an area accuracy

of 1/20th of 1% and a weight accuracy of 1/20th of 1%.

The deadw

eights ha

e been cer

tified tr

aceab

le to N.I.S.T.

with the accuracy of the finished weights better than

1/20th of 1%. To maintain deadweight tester accuracy,

andle the weights with care and keep the piston and

ylinder in clean condition.

The tester should be flushed with a solvent occasionally,

preferably every six months, so that operating fluid is

always clean. This will prolong component life, and provide

rotection against possible sticky action between the pis-

on and cylinder. After cleaning, always lubricate parts

efore assembly.

If a deadweight tester is not used for long periods of time,

or if a piston and cylinder assembly is being replaced, the

iston should be removed from the cylinder and coated

ith the hydraulic fluid, so that it never operates in a dry

tate. When removing or replacing the piston, it should be

rotated back and forth.

Should a piston or cylinder wear excessively, the tester will

leak oil at a high rate, and will not be operable. A new pis-

ton and cylinder assembly should be installed.

Piston wear will result from improper or contaminated

lubrication, excessive dirt, or from several years of

continuous use.

5.2 Cleaning

Both the Tester and Test Pump should be cleaned thor-

oughly whenever the operating fluid is seriously contami-

nated with dirt, grit, or chemicals. A good practice is to

clean the test unit prior to anticipated periods when the

unit will not be in use.

5.3 To Disassemble for Cleaning

(See Figure 2-1, Figure 2-2 and Figure 5-1)

It is necessary to disassemble only those components

which come in contact with the operating fluid. Complete

disassembly is rarely necessary.

a.Remove pipe extension assembly (58) or piston and

cylinder assembly(67) and (79).

b. Then remove lower or back connection pipe assembly

(64, 66).

5.4 Removing Pump Handle and Piston

a.Remove four retaining rings (8).

b. Slide out two clevis pins (9).

c. Remove clevis (10).

d.Lift hand assembly (4) with piston pin (7) piston (20)

O-ring packing (12, 19) and back-up ring (11)

attached to it, out of piston sleeve (6).

. Remove back-up washers (18, 11) and O-ring packing

(12, 19).

f. Unscrew piston (20)

g.Remove piston sleeve (6) and O-ring packing (45, 16)

and back-up washers (46, 17)

5.5

Removing Reser

oir and Fill Tube

Unscrew filler plug (35) from reservoir.

b. Remove gasket (36).

c. Remo

e reserv

oir (5) by remo

ving three screws (24).

d.Twist reservoir to free O-ring packing (21) seat.

e. Remove O-ring packing (21) from body (2).

f. Remove fill tube assembly (23) and O-ring packing (27).

g.Remove plug (22).

5.6

Remo

ving Shuttle V

alve, Shuttle V

alve Plug

and Check Valve

a.Remove set screw (33) and spring (32).

b. Slide shuttle valve piston (31) out of body (2). Operate

back and forth as necessary to dislodge pin (31)

engagement.

Remo

ve shuttle pin (31) by pushing it into the shuttle

valve piston cavity using a plastic shaft less than

⁄

inch (3mm) in diameter.

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 18 19 20

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