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Pump protection against dead headingHelpful Member!(2) 

eeprom (Electrical) (OP)
5 May 12 10:12
I am an EE, and I'm working on a control system to protect centrifugal and vortex pumps from catastrophic failures due to dead heading.  I am going to use temperature as a leading indicator of failure, so I intend to install a temperature switch onto the housing of the impeller.  From a control standpoint, this is very simple: it is just a thermostat.  But given the huge variation in pump sizes and shapes, selecting and mounting a good switch is not so simple.

The best solution I have come up with so far is to use a thermally conductive epoxy to mount to the pump casing.  But this would be a bit of a pain to install, and it may not hold up as well as a bolt.  Tapping into the casing is out of the question.  So I am stuck with the question, "how to mount a switch to the casing of a pump?"

Does anyone know if a switch is already made for this application?
If not, does anyone have any ideas for mounting a switch?

SNORGY (Mechanical)
5 May 12 10:51
I think a flow switch either in the suction or discharge line would be more cost effective and probably simpler.  Then all you need to do is configure the pump run status to come on line before the low flow switch g.oes live.
Yobbo (Mechanical)
5 May 12 12:42
I do agree with Snorgy. Pumps can heat up very quickly adn locally temperature hotspots may occur. These hotspots are determining the possible damage. As soon as your temperature measurement is not at the high temperature spot or doesn't react swiftly enough the pump may be damaged even before your control system will notice it. Principally it is better to detect a lack of flow through the pump as it is the actual cause of the sequence of damages.

Karel Postulart, The Netherlands
Nuon Power Generation

BigInch (Petroleum)
5 May 12 14:31
an FS will also tend to protect against potential cavitation instead of allowing cavitating and maybe flashing while heating up, provided that your flow remains above minimum flow.  Keeping flow above minimum flow is better, but if not, an FS is still better than a TI.

What would you be doing, if you knew that you could not fail?

eeprom (Electrical) (OP)
5 May 12 16:34
I agree that a flow switch would be better.  It was my first recommendation to my client.  But the slurry being pumped is exceptionally abrasive.  A flow switch (like a paddle) probably wouldn't last 6 months.  

Please also note that I am not trying to protect the pump; I am trying to protect personnel from catastrophic failures of the pump.  

hydtools (Mechanical)
5 May 12 17:08
Use a pressure switch or gauge in the outlet to indicate approaching shutoff pressure since pressure is what you are concerned with.  Temperature is after the fact.  And you have decided to not use a flow switch.


SNORGY (Mechanical)
5 May 12 17:42
You could do a non-intrusive device like a Doppler meter with a low flow signal.  Otherwise a pressure switch is another good option as long as there is enough elapsed time allowed to ensure you are detecting a true deadhead situation as opposed to just a transient.
eeprom (Electrical) (OP)
5 May 12 20:55
Thank you for your comments.  I am glad to have this discussion.  I have done a lot of research on this, but I am not confident that I have considered all of the possible setbacks.

A doppler device would be very expensive, especially for a smaller pump.  Remember, the goal is to prevent catastrophe, not to protect the pump.  

The difference in dead head pressure and operating pressure is too small to detect, and the difference will vary depending on the pump and where it is operating on the pump's curve.  

Temperature leads pressure.  The energy of the impeller will be converted to temperature in the fluid as long as the fluid is below saturation temperature.  Once the fluid reaches saturation temperature, then the pressure will start to increase.  

If the pump discharge is 50 psi, then the saturation temperature would be around 300F.  If the temperature switch is set to detect 180F, the pump will shut off before any pressure builds.
BigInch (Petroleum)
6 May 12 0:00
I don't see how temperature is leading pressure.

What would you be doing, if you knew that you could not fail?

clay87 (Mechanical)
6 May 12 0:51
1.  Perhaps don't use discharge pressure for your analysis.

2.  Is the concern that the equipment is going to vibrate/break and hurt somebody or that the pump case is gonna explode from over-pressure?  If the latter, how about a pressure safety valve?

Artisi (Mechanical)
6 May 12 1:07
Have you considered monitoring power input  

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)  

eeprom (Electrical) (OP)
6 May 12 9:11
I have not considered power monitoring, but I have considered current monitoring.  And I found that there is a surprisingly small difference between a loaded pump and a dead headed pump.  So current is not a good indicator.

I've also looked at pressure discs: these were cost prohibitive.

BigInch, pressure leads leads temperature in the same way a boiler works.  The fluid (water) is initially at ambient temperature at 50 PSI (for example).  The energy from the pump, which is constant, adds enthalpy to the water.  While the water is in liquid form, that increase in enthalpy takes the form of heat, at 1 BTU per lb water per degree F.

Once the water reaches it's saturation temperature (~305F), then the input energy starts converting the water to steam.  It takes 1000 BTU per pound of water to vaporize the water.  Once all the water has been converted to steam, it is now dry steam, and the input energy goes toward superheating the steam.  This is where the largest pressure increase comes from, and this is the most critical point for pump failures.

So, according to my assessment, short of a flow switch, temperature will be the first detectable change in the direction of pump failure.
bimr (Civil/Environmental)
6 May 12 9:14
There is probably no physical method to mount a sensor that would also not create a barrier to the flow of heat. You would also be waiting for the pump housing to heat before you would be able to sense the temperature on the outside of the pump casting.

I think Atisi has made a good recommendation to monitor the power input to the pump.
SNORGY (Mechanical)
6 May 12 9:16
If the difference between dead head pressure and operating pressure is too small to detect, I.e. flat characteristic, then flow or power are better measures than pressure.  You would need to know the power draw at operating point as well as at shut-off; depending on efficiency of pump and motor, I suspect power draw would go down as you approached shut off.  My reservations about this are that as you have wear over time in service, I don't have a good practical feel for how repeatable the power measurement is going to be.  Maybe it will always be accurate and repeatable enough to be effective.

Apart from that, mabe a skin temperature RTD on the pump casing is fine.  People do that with exchangers and air coolers all the time.  I would think you would need to do something to compensate for ambient or suction side variations in temperature.  A corresponding RTD on the suction would provide the second measurement to give you the differential.
eeprom (Electrical) (OP)
6 May 12 9:27
The internal fluid pressure will certainly be higher than the casing temperature.  But (in my opinion) the temperature of the casing would be within 25 degrees F of the internal temperature.  My margin of safety is about 100F.  My plan was to use thermally conductive epoxy to mount the switch.  

I am trying to spec this for pretty much any centrifugal or vortex pump.  I don't have a very good plan for fastening the switch.  The switch cannot fall off.  Bolting it on would be ideal, but it would also be unlikely to happen.  

I am assuming that no one in this forum is aware of an existing temperature switch for this intended use.  But if someone has any ideas on how to securely fasten this, I would like to know.

eeprom (Electrical) (OP)
6 May 12 9:58
Why would the differential temperature be valuable?
clay87 (Mechanical)
6 May 12 11:19
To answer your specific question, a couple suggestions:
*  pumps have ports intended for pressure gauges, vents, drains, that are often not needed by the operator and are just plugged.  Maybe you could take advantage of these (and measure fluid temperature directly) instead of adhesive on the exterior of the casing?

* Maybe mount this device using exiting fasteners for pipe flanges or seal housings?  Or does it need to be more strategically placed?

More thoughts:
- A 100 degree difference between the rotor and casing may lead to pump failure regardless of how close the fluid is to its boiling point.  Your concern appears to be over-pressurization, so why not a safety valve?  
- Goulds has an I-alert device that measure pump (bearing) housing temperature.  Not sure how they mount it.
eeprom (Electrical) (OP)
6 May 12 12:06
Thank you for your input.  The use of a thermal well is problematic because the internal fluid is a very abrasive fluid.  The port won't last.  

I will investigate the Goulds I-alert.

SNORGY (Mechanical)
6 May 12 12:53

My rationale is that if you start with say 10 C water and get a 30 C rise in temperature, that might signify the development of deadhead whereas not so if you start with 25 C water.  Thus, if you set the temperature switch at 30 C (one fixed temperature) you don't necessarily have a good reference point from which to establish how much heat is being transferred to the water as a result of the pump work input.

I am not familiar enough with your system to determine how much heat or temperature rise would be bad, but it is more the rise in temperature across the pump that suggests deadhead than simply the discharge temperature by itself.
BigInch (Petroleum)
6 May 12 13:31

Thanks for the thermodynamics lesson. I had no idea that you could boil water without seeing a temperature rise first, at least without first reducing the pressure below vapor pressure isothermally.  It doesn't sound like you're doing that.

Here's the pump lesson for you.  If everything is as you say, you are very near dead head pressure before, or at the same time, or just as you begin generating heat in the fluid.  That's already below minimum flow.  That is the time to shut down, not when you have been boiling fluid for 15 minutes, heating the bearings and burning the seals.  Unless you are running normally at nearly boiling temperature, before you change it to vapor, you will see a temperature increase well before you get to boiling temperature.  Surely you can't mean that you boil the fluid before seeing a temperature rise!  As you say, you've got to heat the fluid to boiling without experiencing a temperature rise.

Max Power and current monitoring won't help, as power and current are probably their lowest at dead head.

If you don't mind running dead head for a few minutes while things get hot and pressure builds up a little higher and it sounds like you don't, at least until it's ready to explode.    Put on a relief valve set a couple of percent higher than dead head pressure, or equal, or 1/2 percent lower.  Recirculate the relief discharge back to the tank.  Put the flow switch on the relief line.

Now.  Sounds like somebody picked a bad pump for your application, or is running it at a bad flowrate.  If you're running so close to dead head pressure that you can't tell the difference from when it's dead heading or not, your normal flowrate is not anywhere near the BEP for a conventional pump, or you'd have to have one hell-of-a-flat pump curve.  Or is it one of those rising pressure to BEP pumps.  You should have some room there for a relief/recirculation valve, at least 10% or something.  How is it that you're normally running so close to dead head that you can't tell the difference.

Your pump doesn't have a relief valve in it now?  That' another way to prevent an explosion BTW.

Can't get a TI on the bearings?

What would you be doing, if you knew that you could not fail?

eeprom (Electrical) (OP)
6 May 12 13:44
I cannot tell if you are being straight or sarcastic.  Of course there is a temperature rise.  The temperature rise continues until the fluid reaches saturation temperature.  At that point the heat input is used to overcome latent heat of vaporization.  While in saturation there is no temperature rise with an increase of heat energy.

Anyway, I have not been very clear.  This concept is not for one application.  This system is a design for any pump regardless of size and fluid type.  The only common is that all pump fluid runs normally below 140F, and all pumps are vortex or centrifugal.

Using current to monitor where the pump is operating is not reliable.  There are too many variations.  The current changes very little at no load.  What changes is power factor.  And that would be expensive to monitor on a wide spread application.

This is a catastrophic insurance policy.  It has nothing to do with saving the pump.  This is to shut the pump down in order to protect personnel.
BigInch (Petroleum)
6 May 12 13:50
Then maybe ask me again when you have a real-life problem.  These solve-all problems for pumps that don't exist, that have flat pump curves, that have abrasive fluids, that don't have relief valves ... well... I'll see if there's a baseball game on. Good luck.

What would you be doing, if you knew that you could not fail?

bimr (Civil/Environmental)
6 May 12 14:01
PD pumps use both a dry running temperature sensor as well as Overpressure Protection device.

Overpressure Protection device is a diaphragm contact pressure gauge with an adjustable contact for maximum pressure.

The Dry running protection device TSE measures the temperature between rotor and stator is permanently sensed thermoelectrically via a temperature sensor integrated in the stator and compared with
the limit value set at the TSE control unit.

When the pump runs dry, the temperature will rise due to the increased friction between rotor and stator. When the set limit value has been reached, the TSE control unit switches off the pump drive and triggers a fault message.

Tayco manufactures surface mount temperature sensors for many applications including pumps. General purpose metal or ceramic encased elements can be laminated in polyimide, silicone, or epoxy.
TenPenny (Mechanical)
7 May 12 9:18
You might want to look into the ITT Goulds 'PumpSmart' products; they use VFD technology, but they have an internal algorithm to allow them to be configured to protect centrifugal pumps against deadheading and cavitation.

I'm not plugging this product, but it sounds like you're looking to do what they have already done, so it's worth a look., I think, and look at the PS200 PumpSmart product.
1gibson (Mechanical)
7 May 12 15:40
Measure temperature increase across the pump with surface mounted thermocouples on suction and discharge piping?

One of the first relevant links in a google search for "differential temperature thermocouple" is:
clay87 (Mechanical)
7 May 12 19:01
On that can look into high precision temperature monitoring such as the Yates meter (  This should tell you where you are operating on the curve but I question its accuracy on a low head pump.  I would expect motor current would be more useful.
stanier (Mechanical)
8 May 12 7:41
An ultrasonic flow switch would cost less than a $1000.

The variable is "flow" so detect "flow" not a symptom of low flow. works on sewage and slurries as well as clean fluids.

Cost of the instrument is less than the engineering.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

eeprom (Electrical) (OP)
8 May 12 7:51
Thanks for all the recommendations.  I think I may include the ultrasonic flow switch as an option.  Flow switches can be so squirrely, especially ultrasonic ones.  You have to make sure the sonic goop stays on the sensors, and that doesn't work so well outdoors.

This is supposed to be catastrophic protection only. Nuisance trips will upset the process, and that will be expensive.
Artisi (Mechanical)
8 May 12 9:57
What is the catastrophic failures you are expecting?

I really don't see what the problem is, there are 1,000's of slurry pumps operating round the world on 100's of different applications with some installed and working under atrocious mis-matched aplications - how many have such sophisticated protection -I would suggest nearly none.
Have you undertaken any research to establish what the likelihood is and how many have suffered catastrophic failure when operating at shut head, again I would suggest very very few?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)  

eeprom (Electrical) (OP)
8 May 12 11:15
I didn't create the problem, I was hired to analyze and solve it.   
stanier (Mechanical)
8 May 12 19:02
If a catastrophe can occur then do the risk benefit analysis before speaking in terms of expense. A magflow meter or Coriolis meter would be the choice if the cost of a catastrophe, in money, life or environmental terms is high.

Define catastrophe? Loss of production, environmental spill, loss of life???

The petrochem industry does a SIL analysis to determine the risks involved with control systems.  

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

BigInch (Petroleum)
9 May 12 11:53
Apparently very much less than the cost of a strap-on flow meter.

What would you be doing, if you knew that you could not fail?

DLite30 (Mechanical)
9 May 12 12:51
I think your best bet would be something like a paddle flow switch, kind of like this.

With a slurry solution it may not respond immediately to a loss of flow, just because of the higher viscosity...i.e. it may take a few seconds to spring back to it's now flow position, but it would be a lot quicker than detecting a temperature rise of the pump casing.
stanier (Mechanical)
9 May 12 18:47
Paddle flow switches last nanoseconds in slurries. By the time you engineer it  and have a team install same the cost of the primary element is miniscule compared to the risks.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

eeprom (Electrical) (OP)
9 May 12 21:39
There have been some very good ideas offered on this topic.  Thanks.  But I would like to argue in favor of a temperature switch in that: 1. It is non intrusive; 2. It is cheap; 3. It is easy to implement in a pump starter circuit;  4. A pump with a 50psi dead head pressure has to reach 300F before it starts to build pressure, and so a temp switch set to open at 180F has a large margin for safety.   
SNORGY (Mechanical)
9 May 12 22:27
Couldn't a pump operating at dead-head against a closed block valve or pipe blockage downstream start to build some pressure immediately coincident with the increase in temperature due to adding horsepower to the fluid that is otherwise (sort of) going nowhere, or is the thermal expansion of the fluid compensated for by the slip back around the impellers?  I suppose it depends on overall head capability, speed and impeller clearances, but I suspect the pressure would rise at least somewhat; perhaps not with a slurry pump (coarser clearances).  But, certainly you would not be expecting to allow the temperature of even a warm slurry to rise to T(sat) at P(shutoff) before you tripped the pump, correct?  Your selection of 180 F is otherwise OK on first glance, but be careful with other components of the pump that might be destroyed by the pumping temperature irrespective of the pumping pressure, such as elastomers, or such as mechanical seals that might require external quench water in order for the pump to be suitable for hot slurries.  Chances are, your temperature setting might be governed more by those limitations than by trying to prevent the pump from exploding due to the pressure rise arising from heat input at deadhead.

While I acknowledge merit in the temperature-based concept, I still think flow is better for you.
Helpful Member!  Artisi (Mechanical)
9 May 12 22:41
I would question if a pump developing 50psi at shut valve could ever achieve anywhere near 300F. Anyway, seems the OP has already decided on temp as the trigger so we should save our breath, shake or nod our heads depending on own thoughts on the subject and leave it at that.   

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)  

eeprom (Electrical) (OP)
9 May 12 22:55
Let's keep it civil, no pun intended.  I'm not making things up for the sake of making my job easier.

I completely agree that flow would be better.  But given the design requirements (to prevent catastrophe), the temperature switch will allow the pump to be ruined, but it will protect personnel.

The pressure of the pump dead head is simply it's shut off pressure.  The pump cannot gain any more pressure unless the pump speeds up (won't happen), or the temperature of the fluid increases to the point that the fluid begins to vaporize (this will happen eventually).  If a pump cavity has water at a pressure of 50 PSI, at what temperature will that water become steam?  Look it up in the steam tables.  It's about 305F.  

SNORGY (Mechanical)
10 May 12 0:24

That is where my reference to T(sat) at P(shutoff) came from.

I will try to put a less electrical spin and more mechanical spin on this topic.

Artisi's point is profoundly all-encompassing.  Unless your system is, for all intents and purposes, adiabatic, you might never get to the point where the water will ever boil.  It might get hot, though.  My point is that hot water in a stagnant column against a blockage will expand with increase in temperature, and in the system that you describe, the only avenue for mitigation of the coincident pressure rise will be in the "slip" of water around the impellers.  That avenue may, or may not, limit your rise in pressure as a result of heat input at deadhead, at least to some degree.  However, I believe it likely that some other mechanical failure will occur before the pump explodes as this operating condition is permitted to continue.  I made reference to failure of elastomers and seals, which may not be perceived to be catastrophic but which will nonetheless render the pump inoperative.  Further, depending on the configuration of the pump, prolonged operation to the far left or far right of BEP (in your case, as far left as you can get) can give rise to shaft deflection and premature bearing failure due to unbalanced radial forces.  If you have a healthy continuous rise to shutoff in your pump characteristic, you might not see load oscillations, but if you are flat or have "droop" in the characteristic near shutoff, you can end up with unstable operation and cyclic loading that can fatigue parts - like the shaft - to failure.  If something like that happens, although you haven't blown up the pump due to overpressure, the failure can be equally catastrophic in nature.

In my opinion, the best indicators of deadhead are, in descending order, (1) low or no flow; (2) differential pressure across the pump; (3) pump discharge pressure; (4) temperature rise per your suggestion.  In the event that you choose Option 4, then I believe it would be prudent to use the high temperature set point that is the lower of your number 180 F or the temperature limit of the weakest link component in the pump that is susceptible to failure at elevated temperature.  That way you mitigate most of the "oil canning" risks with exactly the same safeguard, and the only thing remaining at issue is its set point.
Helpful Member!  bimr (Civil/Environmental)
10 May 12 0:32

I posted earlier about an epoxy mounted temperature sensor. Don't know if you have reviewed that post.

I was thinking that there may be a better alternative than epoxy mounting a sensor. You can actually use a non-contact infrared temperature detector. There is an advantage to it in that you can target the beam on the location of the pump where you expect the temperature rise to occur. The mounting of the non-contact infrared temperature detector should be a little simpler (unless your pump is insulated).

Check this out:
eeprom (Electrical) (OP)
10 May 12 6:47
Thanks for your suggestions.  You bring up a good point of other parts failing prior to casing rupture.  The system is clearly not adiabatic.  

In my estimation, it is a matter of having a constant source of heat energy to a mass of fluid within a steel casing.  The temperature and pressure of that fluid will continue to rise until either the casing is expelling that same amount of heat through convection (steady state), or the pressure exceeds casing.  I am making the assumption that the fluid cannot escape around seals.   
1gibson (Mechanical)
10 May 12 11:20

Well, scratch the differential temperature measurement if there is potential for reverse flow. If heated fluid makes its way back to the suction, differential temperature is obviously no longer an appropriate safeguard.

But on that note, with potential for reverse flow, a centrifugal pump can only maintain the differential pressure of shutoff head. So rather than say a 5 ft section (slug of fluid between pump discharge and valve) heating up and increasing pressure, it will flow back through the pump until suction temp is also elevated, which will decrease your NPSHA, which may lead to cavitation and drop in differential pressure before the pump is able to exceed your pressure rating. Or... Maybe not!

What is the NPSH margin (considering vapor pressure at elevated temp), what are the NPSH characteristics at shutoff, what is the pump Nss, etc. Not really a one size fits all solution, is it?

Unless of course, you monitor differential temperature across the valve! Sufficient distance away that heat conducted through the valve/pipe doesn't allow the readings to converge. I'm running low on what-if's now.

hydtools (Mechanical)
10 May 12 11:38

I would not expect the pressure to rise above the impellar capacity to generate pressure. The casing intake is open to suction and some slip or internal recirculation will occur. Pressure above the impellar capacity will force fluid backwards reducing pressure to shutoff pressure, the impellar cannot generate enough pressure to prevent backflow. Temperature will continue to rise. The casing, or other pressure containing parts, will not fail until the temperature reduces the material strength to no longer be able to hold shutoff pressure.
If vapor is formed, the impellar capacity to generate pressure will be reduced. Vapor would push back into the suction line. You may get suction blowback before seeing mechanical failure.
Just thinking out loud.


lylebrown00 (Mechanical)
10 May 12 18:18

May be of interest:


hydtools (Mechanical)
10 May 12 19:33

lylebrown00, interesting document. Serious pump failures.

Their simple stand pipe solution, where applicable, permits pressure relief out the suction side of the pump and prevents pump burst.

Other solutions presented, where applicable, to release pressure and prevent pump burst.


TenPenny (Mechanical)
11 May 12 7:52

I have known of this happening once. The pump was an ANSI pump, something about a 1x2-10, pumping hot water, running at 3600 rpm with a 25 or 30 hp motor, if I recall correctly. A millwright on his rounds noticed the pump was not sounding good, and that it looked discolored - so he went back to his maintenance shop to get his tools. When he came back, the pump casing was gone - the pump had exploded, and the casing had flown across the room.

We all figured that if he had been about 5 minutes sooner, he would have either been killed or seriously injured. It turns out that both the suction and discharge valves were shut, so the pump was generating steam inside the casing, and once the pressure/temperature exceeded the casing limits, it blew.

That's the only time I've ever personally known of such an event, but reading that attachment, it's not as rare as I would have expected.

hydromarine (Mechanical)
12 May 12 2:33
sounds like the gaurd fabricators may suddenly become busy after reading these threads
SNORGY (Mechanical)
12 May 12 10:26
Shut down on low or no flow...and it doesn't happen.
eeprom (Electrical) (OP)
12 May 12 12:10
One thing to remember is that temperature is a leading indicator of a pressure rise. If you have started to build pressure, you are too close.
hydtools (Mechanical)
12 May 12 15:39
is your piping closed on both sides of the pump in your problem?


SNORGY (Mechanical)
12 May 12 16:29
Of course, flow stops first before anything else happens.
Just sayin...
bimr (Civil/Environmental)
13 May 12 10:37

In reading the incidents, it appears that many of the pump incidents took place over several hours. There is no explanation as to why no one noticed no flow. One would have thought that the no flow would have shut the plant processing down.

In many industrial settings, such events may have caused other catastrophes to occur prior to the pump failure.

Perhaps the operators need the installation of emergency buttons that must be pushed every minute or two similar to what is used on railroad engines. If the button is not pushed, automatic brakes are engaged and an alarm sounds.
SNORGY (Mechanical)
13 May 12 12:28
We might be devoting too much attention to looking for something beyond the obvious here. To me, running a pump at deadhead achieves nothing and only leads to failure. If it was my decision to make, then I would decide that once the flow stops, so does the pump. The rest is just tuning (ramp down, timer, soft start / stop). This has worked 100 % of the time for me to date.
BigInch (Petroleum)
13 May 12 14:42

I thought the same thing about shutting the system down from a completely different trip point. It would seem that an alarm clock might be the best device in this case.

What would you be doing, if you knew that you could not fail?

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