Ashcroft 1305DMh-150 Manuale di installazione e manutenzione - Pagina 11

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the pressure. To check operation pull the shuttle valve

outward, close the release valve and operate the pump

handle several times. When handle resistance is felt, push

the shuttle valve inward and continue pumping within the

range of the test device.

Entrapped air will prevent the pump from operating in the

high pressure valve position or cause it to achieve only

partial pressure. Repeat the above bleeding procedure

as necessary to assure all air is removed. Once air is re-

moved the pump will continue to operate without further

attention providing the reservoir level is maintained.

3.5.3 Making The Test

Turn displacement piston handle (41) to mid-position, so

that it may be used for setting an exact pressure on the

gauge. The displacement piston has internal stops which

prevent unscrewing or accidental loss of pressure.

Clockwise rotation of displacement piston will produce

an increase in pressure; counterclockwise will decrease

pressure.

Prior to taking readings, both gauges should be fin-

ger-tapped lightly at the center of the gauge face, to elim-

inate any movement friction. Note the pressure readings

on the test gauge and the gauge under test. If the pres-

sure indicated on the gauge under test is not equal (within

the tolerance of the gauge) to the pressures of the master

test gauge, the gauge being tested requires calibration.

CAUTION:

Do not pump handle to pressures greater than the pres-

sure range of the gauges connected to the test pump, as

this may damage the gauges.

3.5.4 To Release Pressure

Open release valve slowly (37), until pressure returns to

zero. Do not loosen any connections until pressure in the

gauge tester has reached zero, as indicated on the test

gauge.

If additional gauges are to be tested, close the release

valve when the pressure reaches zero. This will prevent

complete drainage of oil in the tester back to the reservoir.

Unseal the gauge that has been tested by unscrew-

ing adapter nut (62) from connector (60) several turns.

Unscrew the gauge from bushing (59) if used, or connec-

tor (60), and remove.

Remove the test gauge in the same manner as the gauge

under test.

3.5.5 To Dismantle

To replace test pump in case, remove gauges and both

tube assemblies. Put shipping plugs into pump and tighten.

Close filler plug (35).

3.5.6 Operating Fluids

Standard Test Pump:

Any medium weight oil may be used (including automotive

oils S.A.E 10, 20 or 30) S.A.E. 20-W recommended.

Hydraulic Test Pump:

Any hydraulic fluid (silicate or phosphate base). Skydrol or

Pydraul is suitable.

Oxygen Test Pump:

Distilled or demineralized water with a compatible corro-

sion inhibitor added. A .1% solution of sodium dichromate

is a suitable inhibitor.

For normal operation it is not necessary to change the

weight of oil for various pressures. A lighter oil may be

used where low pressures are being checked, a heavier

oil where higher pressures are being tested.

The reservoir can be refilled while the test pump is operat-

ing under pressure.

3.5.7 Caution

Standard testers designed for oil service may not be used

with water for oxygen service.

3.5.8

Hydraulic service testers should not be filled with water or

any oil other than hydraulic fluid. Serious pump failure may

occur due to O-ring damage.

4.0 FACTORS AFFECTING OPERATION OF

DEADWEIGHT TESTERS

4.1 Deadweight Tester Accuracy

Excellent accuracy is possible using the deadweight tes-

ter through analysis and control of certain factors. If the

tester's rated accuracy of 1/10th of 1% is adequate, then

the nominal pressure (sum of the denominations of the

weights loading the piston) may be assumed to be correct.

The pressure normally developed is determined by this

formula: Deadweight Tester Pressure =

Mass of weights plus piston mass

Effective area of piston and cylinder

P = (M-ph) g

= pressure

= mass of the load on the piston

= effective area of the piston in sq. inches, or sq. cm

g/gs = ratio of the value (g) of gravity at the point of use to

the standard value of gravity (gs)

= density of liquid used in test

= difference in level between gauge being tested, and

the bottom of the piston

The deadweight tester is capable of measuring pressures

to proper corrections after analyzing these factors.

4.2 Gravity, Calibrated Weights

Weights furnished are calibrated at standard gravity of

980.665 gals. If precise accuracy is required, the error

introduced by change of weight due to change in gravity at

the locality should be calculated and included in results.

The mechanism of an Ashcroft Pressure Gauge includes

a Bourdon tube and geared movement, which is unaf-

fected by variations in gravity. Conversely, the pressure de-

veloped by a deadweight tester is proportional to the value

of gravity. Readings of this type pressure gauge will cor-

respond to those of a deadweight tester when the tester

is subjected to standard gravity (gs = 980.665 gals. in the

International System). In southern sections of the United

States, the value of gravity may be several thousandths

less than the standard value, if the latitude (Ø) and the

elevation above sea level (a) for an area are known, the

approximate value of (g) in gals. may be calculated from

this formula:

g = 980.632-2.586 COS 2Ø

+.003 COS 4Ø - .000094a

Ø = Latitude (Degrees)

a = Elevation above sea level (ft)

4.3 Effective Measured Area: Chamber

The effective area of the deadweight tester may be de-

termined by the average of the cross sectional area of

the piston and the area of the cylinder bore. This effective

area is affected somewhat by temperature, and by the

elastic distortion of the piston and cylinder when pressure

is being applied. The effective area of a stainless steel

piston and cylinder increases approximately .068% with

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