We just picked up several Otis 21UCL units. But the doors all slam shut. All five of the operators are 6970s.

My question is this! What have you done with these old door operators?
Rebuild, replace or modifaction?

I've rebuilt several 20+ years ago!
I've maintained units that were replaced with operators such as GAL!
And as of recent we maintain a unit that has been modified with a MCE Smart Traq.

Please share your opinions, experiences and thoughts on this...

these operators are affected by the weather if it is cold outside they are slow and you need to adjust the check, with the screw adjuster, conversely,if it is hot they slam, again adjust the check.Using mobile 1 in the check helps to minimize the the weather affect. Of course the best option is to send it to the scrap yard. We used GAL or the old Montgomery operators.

It is a great Door Operator. There are 2 types of control for the 6970 Operator, Saturable Reactor or Resistance control. The procedures for adjusting are very different. First determine which control you have. If you stop leaks the temperature variation can be controlled by using Mobil One Oil in the check unit. Also the big screws on the top ends are checks and there is a horizontal screw in the ends that determines check distance. Straight up and down with the horizontal screw is the Shortest check distance. Rotating the horizontal screw off straight up and down will Increase the check distance. Make sure the oil level is correct or the checks will not work correctly.

I had this operator on my b base equipment..Reynolds and Reynolds makes a nice retro board which eliminates the rheostat controls .The engines can be rebuilt with the check valve ..

Properly adjusted here operators offer smooth control..open/close checks on either side offer great dampening..

Len,
I'll look up the R&R board. Thanks

John Jay,
Personally, I like the MOVFR units. I'm just not sure I'm ready to send these units to the scrap yard. Although I agree with you that the oil temp in the gear box affects the reliability of these operators. I wasn't aware of the mobile one oil. Thanks for you input.

Rolly,
I also think these are good units. They were built to last. Unfortunately today's advancement have made the use of the checks inadequate & obsolete. Although you and John Jay have indicated mobile one oil will improve stability, there are more options. Wouldn't it be a better made unit if the checks were iliminated and it was designed with a VVVF motor and control?

Thank you for reminding me that there were several versions of the 6970 operator. It just so happens there are 4 with the saturable reactors. The last unit is the resistance version.

Thank you for your responses...

I'm leaning toward recommending modifing the existing operators. These units run constantly from early in the morning to early in the evening. And with all the variables that effect the quality of the doors to open & close, I'm just not convinced that there is a happy medium with check valves in the equation. I've been servicing a operator that was modified with a MCE smart traq for 8 years now. The only things we have had to do is check the motor brushes and the oil level.

I'll let you know where this ends up...

JKH not sure where your getting info but the resistance control on the 6970 was not the last version but the cheaper version of the Reactor Control. The 6970 Resistance control was on most Bread and Butter 11&23 UCL Controllers made in the 50's and 60's. 6970 Reactor was still the Premium Operator in 1975 with A Base Solid State Operational and Motion Controllers. I Adjusted them at the Renaissance Hotel at the Renaissance Center in Detroit in 1975 on 1000fpm cars. Watch some of the VVVF control for doors. Some of them when the transistors short they close very fast with nothing to stop them but a circuit breaker which does not always trip.

Rolly,
Sorry, when I said "it just so happens there are 4 saturable reactor. The last unit is the resistance version" I was referring to my first post. In my first post I said there were 5 of the 6970 door operators.

I remember reading one of the tech spec that they were the considered the premier operator from the 50s to the 80s. I use to have an eight bank on a 30+ story in the early 90s. I always thought is was a shame when we ripped them out.

Thanks for the tip on the transistors.

As Rolly suggested these operators are pretty good. Use 10w-30 which should help with temp variation. As suggested the horizontal screw set at the vertical setting is the shortest setting distance from fully open/close. The vertical screw is the intensity setting( how hard it stops). If your doors are slamming, check your oil(even replace it) and make sure you cycle your doors to make sure the levels are right as it needs more to fit into all areas of the gear box. Then set horizontal screw to horizontal as its a good medium setting. Then screw the vertical all the way in. This is a preliminary adjustment and a good starting position. Adjust then to suit doors. If it still slams something else is going on, either supply volts or you have a oil leak in the gear box.

You also mentioned changing to new PDO's. I have found that you can have a lot of trouble finding the right PDO as these old doors are very heavy and the new VVVF's find it hard to pull them up quick enough. More door adjustments tend to have to be made to get them right, even changing car doors. Rolly also talked about transistor shorting making doors fly open/close dangerously. I have had this with Montgomery PDO's where the Darlington resistors shorted and no matter what adjustments were made it didn't make any difference.

Do you like the MCE? We have several..........they do O.K. but their lack of sensitivity and heavy door functions (a lot of times in buildings the first floor hall doors, being used the most are heavier than the other doors from floors 2 thru whatever) are hard to find a happy medium. In other words, the upper doors slam open a little in order for the first floor heavy doors to open smoothly. Seen the 6970s, but not much experience with them. We have a lot of MOVFR and they do really well -- easy to work on, etc.