Chemical admixture relief valve keeps clogging 3

[3sam]

Hi. First post after reading quite a few.

I'm using a simple spring relief valve (Herbert HNVA Link in the output of a peristaltic pump (Valisi FPSH20) to control pressure in the delivery system (3/4" hose, 60m) for fast setting admixture for shotcrete (Sika Sigunit L54-AF MO. Based on aluminum sulphate and hidroxysulphate). Said admixture has a density of 1.44 and a viscosity of less than 80sec on a Ford cup#4 according to MSDS (300cP after searching for a conversion table from Ford cups to cP).

The relief valve I'm using is set to 120PSI when fully open. However is clogging over and over again. The fluid seems to:
1. Need strong agitation before and while pumping, as the solids go to the bottom of the drum. Agitation is maintained regularly to prevent solids from falling down again.
2.The above makes for a thinner fluid before agitation and thicker fluid after. 300cP should be when the fluid is well mixed. Main aplication uses agitated, well mixed product, not suctioned straight from the bottom of the drum, at a distance of 10cm from the bottom of the drum, where there is no separated solids.
3. Leave a sticky residue that is clogging said valve.

Local consultants seem not to understand what I'm doing/talking about, but I think I'll probably need a different and bigger valve for this. Valve is mainly used as to protect the peristaltic pump internal hose from failing catastrophically in the middle of a concrete pouring labor.

Any help and suggestions are welcome

Thanks.
3.

 

[The Obturator]

Some points to consider:

1. Has this relief valve been sized taking into account the high SG and relative viscosity?
Valve may be wrongly sized - too big or small will affect valve operation.
The viscosity may be increasing with the throughput through the valve where it cannot let the fluid flow properly leading to clogging.
Note also that your link to the valve that you are using clearly states ' Relief Valve for Water'!.

2. What is your operating pressure compared to the set pressure of the relief valve?
Typically valves of this design will not reseat (blowdown) up to 50% of set pressure. You need a sufficient margin between operating and set pressure.

3. Are there particles/solids in the fluid when the valve is open?

4. How often has the valve been required to open due to overpressure? if it rarely opens, maybe best to consider a bursting disc, depending on the operating to set (burst) pressure difference.

5. Has this application been discussed with the valve manufacturer?








*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[LittleInch]

What is that picture of?

Can you post a sectional diagram of the valve?
In English?

But this looks like the wrong type of valve to "control pressure"

The high shear of the fluid as it goes through the valve is probably changing its properties. You really need a control valve set to whatever your max operating pressure is.

That valve looks like it is set up for water.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Suggest The line to the control device be flushed with clean solvent ( water??) for a few seconds after the control device has activated. I dont see how you can do this with the current self operated backpressure regulator. Switch out to an on off electrically operated valve that works off a pressure transmitter. And flush with clean solvent for a few seconds with clean water before the EOV close command.

 

[3sam]

1. Has this relief valve been sized taking into account the high SG and relative viscosity?
Valve may be wrongly sized - too big or small will affect valve operation.
The viscosity may be increasing with the throughput through the valve where it cannot let the fluid flow properly leading to clogging.
Note also that your link to the valve that you are using clearly states ' Relief Valve for Water'!.

2. What is your operating pressure compared to the set pressure of the relief valve?
Typically valves of this design will not reseat (blowdown) up to 50% of set pressure. You need a sufficient margin between operating and set pressure.

3. Are there particles/solids in the fluid when the valve is open?

4. How often has the valve been required to open due to overpressure? if it rarely opens, maybe best to consider a bursting disc, depending on the operating to set (burst) pressure difference.

5. Has this application been discussed with the valve manufacturer?

1.Valve wasn't sized according o any parameters. It was an emergency install where whatever was better than no valve. We want to replace for the right one asap.

2. Operating pressure will be around 40psi. Set pressure is 120PSI. I think this application demands a safety valve, as the flow metering at the end of the hose is critical.

3. The liquid solids go to the bottom of the drum when not stirring for more than 1h, and it leaves a sticky residue as it passes through hings.

4. The valve is required to open many many times in operation as follows: When the nozzleman closes the admixture valve, the system raises pressure because the pump doesn't stop.

5. Not discussed. It was a recommendation from a local salesman, as a quick try.

 

[The Obturator]

You might want to look at a pressure relief valve designed to handle high viscosity fluids on pumps. One such possibility is a high flow diaphragm relief valve. This may be your answer, but give the vendor all the necessary data to confirm the application, particularly, the flow rate. One example of such a valve can be found here:

http://pumpsupplyinc.com/wp-content/uploads/Lit-PRHF_Imperial.pdf

*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[LittleInch]

I'm struggling to understand how this was though to be able to work without a relief system if the flow can just be turned off or reduced in flow without turning the pump off. did you burst a lot of peristaltic pump hoses?

I can only imagine that the pressure rise will be very rapid indeed so might be better to have some sort of continuous flow going around a loop with a back pressure valve maintaining a pressure of 40n to 50 psi.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Btw, that "relief valve" image you posted looks like a safety valve, not a regulator.
The entire relief line should be flushed out with clean solvent to prevent this shotcrete from solidifying in this line and PSV when the line is stagnant.

 

[3sam]

Thanks for the input guys.

Haven't bursted peristaltic pumps hoses (yet), the system was made with the relief valve output going back into the source container. Worked wonders when water testing, horrible with actual admixture.

Tha Shotcrete does not flow through this line. Is only admixture. What goes there.

I am thinking into setting the VFD of the pump to detect a rise in current (when system raises pressure when the nozzleman closes the admixture valve) and so turn off the pump until pressure drops again.

Also considering a gauge with pressure transmitter sontonset the VFD to slow down or completely stop when pressure reaches a certain point.

 

[georgeverghese]

Okay, so the pumped up admix is used as the motive stream to educt the shotcrete. And this safety valve is on the admix line. And it is this alum sulphate - hydroxy sulphate mix in water that is bunging up the safety valve.
If you do have VFD for this pump, then a pressure transmitter-controller with setpoint at 40psi to cascade into pump speed would work as suggested, and avoid activating this safety valve.
A safety valve goes pop-pop, and is no good for pressure control. So with the current setup, it would be better to hookup a self operated pressure regulator in parallel with this safety valve to get smoother control.
Alum sulphate is often used to precipitate calcium and magnesium in raw water treatment operations, so if your water has high TDS (total dissolved solids), then the resulting calcium and magnesium sulphate precipitates would cake up in the safety valve. You would far less clogging in the PSV with soft water in the admix.

 

[FacEngrPE]

I suspect unless you use a large diaphragm paper pulp / sludge duty pressure transmitter with some sort of flushing arrangement, you will have difficulty getting transmitters to survive this service long. But this is close to a positive displacement application, so torque will have a consistent relationship to pressure.

It should be possible to match a gauge pressure (on water) with a torque (or current) measured by the VFD. Then set the VFD to run in constant torque mode. The shortcoming with this method is that the no flow condition = zero R/M = Zero Hz which usually overheats a motor not selected for this service, or trips the I[sup]2[/sup]*t protection.
The drive must be programmed to lower speed very fast when torque>target. Not all drives can do this.