dash pot?

[steveng]

:-? what is a dash pot used for?
is a magnetic underload relay the same as a dashpot?

i have some at work, they are used on a lighting control circuit.

 

[mdshunk]

The only dashpots I know about are little shock absorbers used in motion control applications to prevent overrun from damaging equipment.

 

[sparky_magoo]

:-? what is a dash pot used for?
is a magnetic underload relay the same as a dashpot?

i have some at work, they are used on a lighting control circuit.

A dash pot is a dampening device used in a SU carberator. They were used on vintage Jaguars, and other British sports cars.

Hitachi clones of SU carberators were also used on Datsun clones of Eueropean race cars. I love them.

I eventually upgraded to side draft Webers on my Datsuns.

Hearing "dashpots" reminded me of the good old days.

SU's were so easy to "sync."

 

[rattus]

Hunk has it:

Hunk has it:

The only dashpots I know about are little shock absorbers used in motion control applications to prevent overrun from damaging equipment.

Dashpots are pneumatic shock absorbers, and the proper term for their action is "damping" if that makes any difference to anyone.

The old, lever operated adding machines used dashpots to prevent the operator from jerking the lever too sharply, then controlled the return motion of the lever as well. Those were the days because I was a youngster then!

 

[mdshunk]

I wonder if those pneumatic time delay accessories that you can put on contactors are also called dashpots? Maybe so. I remember some old Agastat relays I used to use that had a vacuum type of time delay on them.

 

[jim dungar]

Oil-filled dashpot "time-delay" overload relays were not un-common on both circuit breakers and motor starters. They were difficult to regulate (set the time delay) and required regular maintenance of their oil level.

Static trip devices (electronic) replaced dashpots in the early to mid 60's, although some old equipment is still in service.

 

[augie47]

dash-pot

dash-pot

Oil-filled dashpot "time-delay" overload relays were not un-common on both circuit breakers and motor starters. They were difficult to regulate (set the time delay) and required regular maintenance of their oil level.

Static trip devices (electronic) replaced dashpots in the early to mid 60's, although some old equipment is still in service.

A few weeks ago, I saw an old baler used for baling cardboard that was still using a dash-pot relay in a motor current circuit to shut-down the motor when the current indicated the bales were thoroughly compressed.
The maintenance foreman said a recent call to the manufacturer almost put them in shock when he provided a serial number of 27 (turned out it was vintage 1950's)

 

[steveng]

jim's got it!

jim's got it!

Oil-filled dashpot "time-delay" overload relays were not un-common on both circuit breakers and motor starters. They were difficult to regulate (set the time delay) and required regular maintenance of their oil level.

Static trip devices (electronic) replaced dashpots in the early to mid 60's, although some old equipment is still in service.

jim, what is purpose of a dash pot, used in a lighting control circuit?

this dashpot coil is 277v and the relay contact is feeding a 1 kva xfmr
pri 277 and sec 120/240. i am not sure if it works, but it was installed in 77.

the lighting contactor is 4 poles 277v, 2 of the circuits are from and emergency generator, for lighting.

 

[jrclen]

I ran across dash pots using air and an adjustable orifice for controlling flow detectors on a sprinkler system in the mid 70's. The idea was to keep water surges from setting off the fire alarm system. If the paddle moved, the contacts wouldn't close until the dash pot timed out. So, on your lighting circuit, I would look toward a delay of some sort being designed into the circuit.

 

[Jraef]

Dash pot relays were often used as overload relays that would provide a delayed reaction to an instantaneous current surge, but eventual tripping if the increased current continued for a time. There was a heater coil in a pot containing oil, the heated oil would expand and flow through an orifice to a plunger that would eventually trip a spring loaded contact. If the current went down and the heater coil cooled off, the oil would flow back into the pot. You could change the delay time by using an oil with a different viscosity, usually designated by color. So for example if you wanted a 10 second delay, you used a red oil, 20 seconds was a green oil etc. etc. (I don't really remember the color codes and values any more, that was 30+ years ago for me). They stopped using them in the late '70s because the dashpot oil had PCBs in it and was highly flammable if it leaked. Most likely on a lighting transformer system it was used to prevent long term overloading of the transformer, but allowed temporary overloading as HID ballasts were striking at the beginning of the day.

They were pretty much replaced first by eutectic melting alloy relays (a.k.a. solder pot relays), then again by bimetallic thermal relays, now by solid state current sensing relays. Don't re-use them, you can get in trouble from the hazmat people.

 

[jim dungar]

They were pretty much replaced first by eutectic melting alloy relays (a.k.a. solder pot relays), then again by bimetallic thermal relays, now by solid state current sensing relays. Don't re-use them, you can get in trouble from the hazmat people.

Dashpot overload relays were used concurrently with both eutectic melting alloy (Square D standard design since the early 40's) and bimetallic (AB standard design at least since the 40's). Dashpots were capable of handling very high currents, both in measuring and in switching.

The last dashpots I worked with were simple solenoid/plunger style units used as overcurrent relays on a baler, the oil slowed down the speed that the plunger moved providing a time delay. The speed of the relay was adjustable by opening/closing holes in the plunger as well by changing the viscosity of the oil.

 

[brian john]

Dash pots were utilized in early design 480 VAC GFP (among other things). These were oil-less, magnetic used in a ground return style GFP, problem was these were never tested and the ones I have tested over the years had trip times in the 5-10 second range. If you took the replay apart the settings were Min-Max*.

Another common use of dash pots was in chiller starters as overloads, (long time operation). These also had time adjustments (Min to Max)* and were additional delayed with oil.

*Some equipment actually had the documentation that gave the time delays in correlation to the Min-Max settings, but most often this documentation was lost/trashed/never read.

 

[coulter]

...this dashpot coil is 277v and the relay contact is feeding a 1 kva xfmr
pri 277 and sec 120/240. ...the lighting contactor is 4 poles 277v, 2 of the circuits are from and emergency generator, for lighting.

I put in a few in the early 70s as part of a relay control schemes. Some were additions to a contactor to slow it dropping out - called "tail-piece timers. Prevented relay races in control systems.

carl

 

[lowryder88h]

Dashpots

Dashpots

Dashpots, That was one of my essay questions on my masters test back in 1978, Jim is correct in his explaination. The only reason that I knew what they were is that as an apprentice in the mid 60's the company I worked for did most of the electrical work at the old factories in our area. Today I feel that that type of apprenticeship is "PRICELESS"

 

[steveng]

thanks for the replies

thanks for the replies

you guys have helped a great deal, we have several of these around lighting contactors, i could see the little oil bottle left inside the enclosure, but i could'nt figure out what the devices were doing,

but thanks to you, it make sense now.

in this particular application i believe what they were trying to accomplish is what you have previously stated.

 

[steveng]

jraef

jraef

Dash pot relays were often used as overload relays that would provide a delayed reaction to an instantaneous current surge, but eventual tripping if the increased current continued for a time. There was a heater coil in a pot containing oil, the heated oil would expand and flow through an orifice to a plunger that would eventually trip a spring loaded contact. If the current went down and the heater coil cooled off, the oil would flow back into the pot. You could change the delay time by using an oil with a different viscosity, usually designated by color. So for example if you wanted a 10 second delay, you used a red oil, 20 seconds was a green oil etc. etc. (I don't really remember the color codes and values any more, that was 30+ years ago for me). They stopped using them in the late '70s because the dashpot oil had PCBs in it and was highly flammable if it leaked. Most likely on a lighting transformer system it was used to prevent long term overloading of the transformer, but allowed temporary overloading as HID ballasts were striking at the beginning of the day.

thanks for the explanation, after looking closer at this, i can see you are right,
this application was used to bring on some 120v lights that are in a stairwell,
that are next to hid fixtures 277, the incandescent lights were on instant, and delayed off, allowing the hid fixtures to reach full brightness. the dashpot was connected to a relay contact that is feeding the primary 277 to a .250kva xfmr, which powers the 120 incandescent lamps, there are only 3 120v lamps per stairwell, in a 2nd floor bldg.

makes good sense now, thanks, i appreciate the help i receive here