Agilent 1050 very low erratic pressure

[sllimbri]

What would cause low and erratic pressure, fluctuating from 4-40bar? It was consistantly running at 250 bar after the pump overhaul. I have verified flow at 2ml/min out of the pulsation dampener. There are no leaks. The seals and pistons and check valves were all replaced. I replaced the frit. I am running 50/50 water/meoh.

[Jackus]

I supposed you properly purged your pump. Have you tested leaking of AIV valve (active inlet)? When you suck in bigger air bubble into PTFE hose from solvent reservoir - is this bubble jumping towards pump only? When not, exchange AIV cartridge or whole AIV valve (when you have older version).

[grzesiek]

"I have verified flow at 2ml/min out of the pulsation dampener." - does it mean that you see mobile phase flowing?

I usually suspect inlet or check valves when I see this

[sllimbri]

An air bubble introduced in the line goes towards pump. I have tried two different AIV's. No help. Check valve were replace with new. No help. I set flow rate at 2ml/min and I get 2ml/min out of dampener. Flow is about 1ml/min from purge valve side of pump. Purge valve was cleaned/sonicated. Frit is new and clean.

[tom jupille]

The pressure depends on the flow rate and on the flow resistance of the system. If you are collecting immediately at the outlet of the pump (no column connected) there will be negligible flow resistance and you will see negligible pressure.

[sllimbri]

I disconnected the column only to check flow. With everything connected, pressure and flow are low. I'm looking for why.

[sllimbri]

I also plugged the output of the pump and the pressure still does not go high.

[Bruce Hamilton]

Several possible causes..

1.Air bubble in pump inlet valve line - root cause could be mobile phase degasser not working, mobile phase mixer ( if low pressure mixing - I don't know 1050 ), partially blocked solvent reservoir sinters ( from buffer salts ).

I'd flush the system with a single phase in all pump channels ( water, methanol, or acetonitrile ), and pump that through and see if pressure increases.

2. Solid deposited on pump valves from buffer. Flush with lukewarm water.

3. Leaking pump seals ( if overhaul is recent, shouldn't be a problem ), possibly due to buffer if seal wash isn't present. Look for liquid from plungers, and ensure solvent reserviors are well above pump.

I'd put a guard column in place and check pressure versus flowrate using water in each channel.

Please keep having fun,

Bruce Hamilton

[sllimbri]

1) solvent sinters removed to eliminate that as casuse...no help, also running straight meoh right now during diagnostics. will try ACN.

2) changed pump valves...no help

3)no visible leaks, reserviors up real high....no help

thanks.

[Jackus]

Difficult to answer when not in front of instrument.

There must be something what we overlooked. Let me summarize possible causes:

1. inlet frit - when removed, problem not solved
2. AIV valve - seems to be OK
3. pistons and seals - leaks not visible
4. Outlet ball valve - exchanged
5. Purge valve - if not leaky, not related to your problem
6. Pulse dampener - probably not related to your problem
Other parts of your system are not important

In your situation I would sonicate Outlet ball valve first in 50% water/methanol and test again.
When you disconnect capillary to column inlet and increase flowrate up to approx. 5ml/min is the mobile phase stream steady?

[coffee bean]

I would check if the pistons are really moving properly (maybe there is a problem with the motor as this is an old LC).

If you have another working 1050, try exchanging the pump heads. That could give you a hint.

Best of luck.

[Jackus]

I would check if the pistons are really moving properly (maybe there is a problem with the motor as this is an old LC).

If you have another working 1050, try exchanging the pump heads. That could give you a hint.

Best of luck.

I think that there is not problem with Metering drive assembly but idea with switching of complete pump heads can help us a little

[sllimbri]

1) ran straight acn for 3 hours last night...no help
2) piston are moving because I can look under pump head and see the springs.
3) no spare unit to use for parts exchange.
4) disconnected line to column and turned pump up to 5ml/min. Flow is not constant. It squirts then stops...squirts then stops...etc.

[Jackus]

4) disconnected line to column and turned pump up to 5ml/min. Flow is not constant. It squirts then stops...squirts then stops...etc.

I think there is problem with Outlet ball valve or pistons/seals. It seems that visit of Agilent CE is necessary

[Bruce Hamilton]

Pulsating flow suggests air, a faulty check valve ( inlet or outlet ) or leaking seals, however I would expect the flow to be lower than nominal.

If one side isn't working, the flow should be half of nominal. If one side is partially working and the other is OK, the flow will be somewhere between 50-100% of nominal. You should try to get the nominal flow at maximum flow, and then check lower flowrates. If the check valves are faulty, or the seals leaking, the effect is more visible at lower flow rates ( < 1 ml/min ).

I would put a restrictor ( eg guard column ) on the outlet, as sometimes dodgy outlet valves don't seat correctly unless they see a significant backpressure. The same may apply to new piston seals.

If the problem goes away with some backpressure you need to repeat the "bedding-in" protocols.

I'd still go down the path of flushing all pump channels with warm solvent before calling in the service technician.