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2. Abnormal Pressure

A change in the operating pressure is a sign that there may be a problem. Choose the category below that best fits the symptoms and follow the suggestions to correct the problem.

A. No Pressure Reading, No Flow

Possible Cause	Solution

1. Power off	1. Turn on power
2. Fuse blown	2. Replace fuse
3. Controller setting or failure	3. a. Verify proper setting
	b. Repair or replace controller
4. Broken piston	4. Replace piston
5. Air trapped in pump head	5. Degas solvents: bleed air from
	pump, prime pump
6. Insufficient mobile phase	6. a. Replenish reservoir
	b. Replace inlet frit if blocked
7. Faulty check valve(s)	7. Replace check valve(s)
8. Major leak	8. Tighten or replace fittings

B. No Pressure Reading, Flow Is Normal

Possible Cause	Solution

1. Faulty meter	1. Replace meter
2. Faulty pressure transducer	2. Replace transducer

C. Steady High Pressure

Possible Cause	Solution

1. Flow rate set too high	1. Adjust setting
2. Blocked column frit	2. a. Backflush column (if permitted)
	b. Replace frit
	c. Replace column
3. Improper mobile phase;	3. a. Use correct mobile phase
precipitated buffer	b. Wash column
4. Improper column	4. Use proper column
5. Injector blockage	5. Clear blockage or replace injector
6. Column temperature too low	6. Raise temperature
7. Controller malfunction	7. Repair or replace controller
8. Blocked guard column	8. Remove/replace guard column
9. Blocked in-line filter	9. Remove/replace in-line filter

D. Steady Low Pressure

Possible Cause	Solution

1. Flow set too low	1. Adjust flow rate
2. Leak in system	2. Locate leak and correct
3. Improper column	3. Use proper column
4. Column temperature too high	4. Lower temperature
5. Controller malfunction	5. Repair or replace controller

E. Pressure Climbing

Possible Cause	Solution

1. See Section C	1. See Section C

F. Pressure Dropping to Zero

Possible Cause	Solution

1. See Sections A and B	1. See Sections A and B

G. Pressure Dropping, But Not to Zero

Possible Cause	Solution

1. See Section D	1. See Section D

H. Pressure Cycling

Possible Cause	Solution

1. Air in pump	1. a. Degas solvent
	b. Bleed air from pump
2. Faulty check valve(s)	2. Replace check valve(s)
3. Pump seal failure	3. Replace pump seal
4. Insufficient degassing	4. a. Degas solvent
	b. Change degassing methods (use
	Degassex on-line degasser)
5. Leak in system	5. Locate leak and correct
6. Using gradient elution	6. Pressure cycling is normal due to
	viscosity changes

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