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Volume Expanders for Liquid Lock protection?

Volume Expanders for Liquid Lock protection?

Volume Expanders for Liquid Lock protection?

(OP)
Is anyone familiar with these?

Our management is really pushing us to use them in a new design. We currently use small in line style relief valves. But they are wanting to cut down on maintenance costs and somebody presented these as a magic bullet to them and now they are pretty much dead set on them.

The manufacturer is claiming infinite cycle life, but I doubt that due to high cycles it will probably see and that these things have bellows inside.

Any help would be greatly appreciated.

RE: Volume Expanders for Liquid Lock protection?

I have no idea what you mean by liquid lock, or volume expanders, but I have worked with bellows.

A well designed, properly applied and properly installed bellows still has a finite life. Manufacturer's reps and salesmen have been known to make ridiculous and unsupportable claims, but a manufacturer who claims infinite cycle life for any device containing a bellows has clearly not done the math. ... probably because they haven't been in business long enough for the field returns to start pouring in. When that deluge starts, they'll fold their tents and start up in another business for which they are equally unqualified.

Infinite is a really, really big number.


Mike Halloran
Pembroke Pines, FL, USA

RE: Volume Expanders for Liquid Lock protection?

I suspect they are something along the line of a pulsation damper for plunger style pumps. Korichnevijgigant, do you have a make and model or a URL to a supplier?

RE: Volume Expanders for Liquid Lock protection?

(OP)
Thanks for the response guys.

when I say liquid lock, I mean having a line filled with liquid and on all entrances and exits of the line section there are closed valves, so due to thermal expansion of the liquid there will be an overstress condition.

Here is a link to the company they are steering us toward. http://www.flexicraft.com/Hydropad_Accumulator/

I am also very skeptical about their claim for infinite cycles, by very nature the 300 series stainless will work harden and eventually meet its fatigue limit and the bellows will rupture.

currently we use small in-line style relief valves to relieve the pressure caused by the thermal expansion, but due to our site's safety program, we have to take these relief valves every 3 years to be serviced, and since the propellants we work with are pretty toxic, this is not as simple as pulling them out of the system. We have to get the technicians in total encapsulation suits with breathing air.

Any thoughts?

RE: Volume Expanders for Liquid Lock protection?

You have to do a credible scenario analysis. The accumulators have proven to be very effective at preventing overpressure due to thermal expansion, BUT ... Few company policies will allow them to be installed without an isolation valve (the only time I've ever seen it allowed was between the suction and discharge valves of a triplex pump). So is it credible for the isolation valve to get shut inadvertently? Maybe. You have to see if procedures are adequate to prevent it. Is it credible for the area around the bellows to become liquid-full from condensation? I've seen it happen. If it is credible then you still need the PSV and you still need to test it.

From an operational viewpoint, I never consider a lifting safety device as "normal". The accumulator can shift small transients from a PSV event to a non-event. That is a good thing regardless of other issues. From a PSM viewpoint, I don't think it meets the red-face test.

As to "infinite" cycles, an ant sees a brick wall as "infinite". I would just take that as sales hype meaning "the devices are pretty rugged and will last a good long while".

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

RE: Volume Expanders for Liquid Lock protection?

Did you know that Corvairs had thermostats?
Yep, on the hot side of each cylinder bank, a welded bellows very similar to what's in the device proposed, filled with something that expanded at the normal operating temperature, linked to a butterfly door that restricted airflow out of the engine until it warmed up.
They worked great.
The longest I ever got one to last is about 6 months.
Diagnosis was easy; if the door was not fully open after the car had run for a while, it was time for a new thermostat.

What's being proposed to you looks just like a common jet pump tank, except it uses a welded bellows instead of the bladder.
Diagnosis of bellows failure is not so easy, unless the fluid within is reactive with the gas used for pressurization. For nonreactive combinations, a failed bellows has no particular effect; it just becomes a gas over liquid accumulator.

Now, if Management is already sold, you can't prevent installation of the Hydropads. You might be able to pressure the mfgr into providing a test procedure to verify integrity of installed units. At the very least, provide isolation valves so you can replace them.


Mike Halloran
Pembroke Pines, FL, USA

RE: Volume Expanders for Liquid Lock protection?

I don't think that the accumulator can replace the relief valve but I would need to know more about your design.

An accumulator with metal bellow only makes sense (from my point of view) if you are handling hot fluids or very high pressures and expect small expansions only. Otherwise a bladder style accumulator with rubber bladder is a much cheaper alternative.

RE: Volume Expanders for Liquid Lock protection?

It sounds like he has some serious fluid-compatibility issues. Reactive fluids don't do well with rubber for the most part.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

RE: Volume Expanders for Liquid Lock protection?

(OP)
The bellows has to be stainless, we do have serious material compatibility issues with the propellants.

The system is rated for 300 psi, the supply is a 3000 gallon vessel and we have 2in sch40 lines manifolding out underneath the vessel, and these lines have valves, which cause us this problem.

We also have the issue of having to hard fill the system (no gas bubbles allowed) and I dont know how the bellows will work with this, and further making this a problem is that the bellows has all those little corners which we are usually not allowed to have, because these collection points can build up residue and contaminate later tests

RE: Volume Expanders for Liquid Lock protection?

I'd think you would still need to pull the accumulators every so often, and check for leakage (the crevice where the bellows edges are welded will tend to corrode pretty quickly I'd think, as it is difficult to believe much cover gas gets in there during welding). Now think about how you decon the valves, to make them safe for rework, and how you would decon these bellows devices, with all those crevices to trap propellant, and the probably much large held volume for the nasty stuff. I'm not sure the bellows accumulators will do much, other than limit the amount of venting due to small, short transients, as zdas mentions, but maybe that is worth the trouble if it means fewer concerns about vented nasty stuff. If this is hydrazine, or one of the variants of it, you could use an epdm rubber bladder, or epdm-sealed piston or epdm rolling diaphragm. You would still need to service it, but the thing would be easier to disassemble and decontaminate.

RE: Volume Expanders for Liquid Lock protection?

(OP)
The media for the systems we will be using these accumulators are Dinitrogen Tetroxide (N2O4) and Monomethylhydrazine (CH6N2)

The way we have done this for a long time, is to have a common captured vent manifold running to all the "liquid lock" locations so venting the said nasty stuff isnt a big deal.

In my mind this would work if it was a storage system, but this is a test article supply system for hot firing and just gives us to many headaches

RE: Volume Expanders for Liquid Lock protection?

I guess I should ask if your system is required to be built and maintained to any design Code. You might want to check with your authorized jurisdiction before you replace your relief valves if that is legal. Just suggesting.

Patricia Lougheed

******

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RE: Volume Expanders for Liquid Lock protection?

(OP)
We are a federal facility, and we have a policy directive stating that we must comply to "relevant national consensus codes"

In another department we have alot small volume expanders installed, but those are tiny systems that are indoors, and locked up for very long periods. they have no "fill hardness" requirements.

Alot of the pressure from management has come with that departments "years of successful operation" in using this type of pressure relief protection

RE: Volume Expanders for Liquid Lock protection?

Korich,

I would agree, for a hot fire system, there just isn't enough time involved to worry about it. If a thermal transient, i.e. post-firing soak, caused problems, the vent is a better solution. A worry with any trapped volume of propellant (e.g. an accumulator) is the inevitable degradation of the chemical due to the very large contact areas between the fuel and the accumulator vessel walls, and what the effect on thruster performance might be due to the potential for having some mixing of degraded propellant with the stream flowing from the fuel tanks.

"In another department we have alot small volume expanders installed, but those are tiny systems that are indoors, and locked up for very long periods. they have no "fill hardness" requirements. Alot of the pressure from management has come with that departments "years of successful operation" in using this type of pressure relief protection "

That's different. The 'other department' sounds like they are doing material compatibility testing and/or storage testing of propellants. There, the goal is to determine corrosion rates of container materials, and/or degradation rates of the propellants, during long term storage, and the only way to measure the progress of such tests in-situ is to measure volume expansion with an accumulator, or by the pressure rise in a trapped volume (which creates risks of explosion, but minimizes the change in exposed area of the propellant to container surface). Both test methods avoid compromising the results by an uncontrolled release of reaction products. The latter method was used by a former employer to conduct compatibility tests with hydrazine fuels; the closed containers were pyrex vessels with a trapped nitrogen gas column. And, yes, these would occasionally rupture, and release the toxic fuel vapors, which was a drawback of that method - but it was planned for, and systems were put in place to contain the releases.

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