Thermal Expansion-Bladder Compensators
Thermal Expansion-Bladder Compensators
(OP)
My question is on thermal expansion compensators that have bladders precharged with N2 on the unwetted side. What is the hazards with having the charge too high or too low of a pressure relative to the normal operating pressure of the system? Would too high cause not enough volume to go into the compensator? Would too little cause the compensator to fill even while pumping (if compensator is vertically mounted and no valve on the bottom while pumping through main lime)?
Any learning would be helpful.
Thanks.
Any learning would be helpful.
Thanks.





RE: Thermal Expansion-Bladder Compensators
Doug
RE: Thermal Expansion-Bladder Compensators
We have a styrene line that feeds styrene through a pump during normal operations. When its not running, there is a blocked in section of pipe that can be heated and expands. If a expansion dampner is put in, this would help to decrease the pressure in the line.
Thanks.
RE: Thermal Expansion-Bladder Compensators
Good luck,
Doug
RE: Thermal Expansion-Bladder Compensators
Remember that when the bladder is in service, the N2 side pressure is the line pressure (when line pressure exceeds charge pressure). If this is a user fillable system, the process side should be depressured and the bladder pressure checked periodically (annually). We had one burst due having the N2 charge slowly leak away leaving no room for thermal expansion.
This servicing may require an isolation and bleed valve if the protected piping cannot be depressurized, but I feel these devices still offer some advantages to thermal relief valves for areas where there is no satisfactory discharge location. We have used in tank farm areas, etc.
best wishes,
sshep
RE: Thermal Expansion-Bladder Compensators
Why would the N2 leaking away into the process cause no room for thermal expansion? The N2 gas still should compress in the tank, allowing the volume of a liquid to rise in the expansion tank.
Why is the bladder even needed in an expansion tank of this sort? Why not just have a N2 blanket on the vessel lower than the normal pressure of the system.
Thanks.
RE: Thermal Expansion-Bladder Compensators
Answer#1, If N2 is leaking into the process then you have a hole in the bladder and your accumulator is in need of a replacement bladder (if a reparable type), however, the leak I was talking about is a slow leak out the fill stem and to the atmosphere. Envision a completely flat bladder inside an otherwise totally liquid full vessel- i.e. expansion capacity is zero. In any event some regular checking of these devices is required.
For the type of device I am familiar with see (has plenty of sizing data for different applications):
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Answer#2, there are vertical mount devices that don't use a bladder, but they generally need a float type valve at the base to prevent N2 leaking into the process during low process pressure. Using an atmospheric pressure initial charge for a bladder-less accumulator would require a vessel too large for many applications. Also some N2 would dissolve away over time requiring the at least the same (but probably more) frequency of preventative maintenance as bladder types.
best wishes,
sshep
RE: Thermal Expansion-Bladder Compensators
I agree with your comment and didn't mean to suggest otherwise. You must figure out the useful (available for expansion) volume of the expansion bottle and use that and not the complete volume of the bottle in your calculations. Since it is easy to err in the calculations and since there is a bit more to this technology than may be apparent, I'd always get a "reality check" from the vendor. Also, always have a working pressure gauge on the nitrogen side of the bladder. It will help with troubleshooting (which is mainly determining if the bladder is leaking). Incidentally, some of these devices use pistons rather than bladders.
HTH,
Doug
RE: Thermal Expansion-Bladder Compensators
When I addressed above post, I actually mistook you for the original poster (RBJ). Your comments are right on. Thermal expansion can be analyzed by simple "isothermal" compression of the gas in the bladder, which is easier calculation than a pulsation dampener application where adiabatic compression is the more appropriate basis.
In addition to your recommended gage on the bladder side, it is also recommended to include a isolation valve between the bottle and the process, and a bleed. The routine preventative check is to isolate, bleed down process pressure, and check the bladder pressure. Incidently I see that my fluidpower link recommends an inspection frequency of 6 months.
best wishes,
sshep
RE: Thermal Expansion-Bladder Compensators
Thanks
RE: Thermal Expansion-Bladder Compensators
htt
Look at the information on accumulators at this site.
Look around at the links and associations on this site as there is wealth of information. This include Pulse Guard, Liquid Dynamics, Shock Guard , and several others. The only problem is that it's a little convoluted.