As more and more brands introduced pulley type self-locking descenders, rope access technicians

are dazzled by so many products. You know, before we only had MPD to choose, but things are

quite different now. Maybe it is the reaction by manufacturers to the markets. They smelt there’s

no competitors to MPD from rope rescue competitions in recent years.

This article compares different pulley type self-locking descenders on efficiency and their functional

differences. I hope it’ll help you.

Hauling a victim is one of the most used techniques in rope rescue. In the past, as a IRATA worker,

I always used an ID to set up a 3:1 hauling system. As you know, there’s a lot of friction in ID, which

lead to a very low efficiency. Until MPD appears, hauling system is much easier than before. MPD was

first introduced to the market by CMC in late 2000s.

But for cavers, nobody is willing to take such a bulky into caves. In addition, the sands, water, mud

will be a disaster to MPD. Due to unique environment, cavers have a clever way to pull up a load.

Combined with a progress capture pulley (such as Petzl micro traxion) ,a caver could use his weight

to balance the load of victim and raise him easily. However, it’s a little bit difficult for the rescuer to

lower the victim.

Different fields and history have evolved different application of equipments.

Pros and cons

	Progress capture pulley	Classical self-locking descender	Pulley type self-locking descender
Typical product	Pro traxion	ID	MPD
Pulling efficiency	very high	very low	high
Big load(two persons)	No	yes	yes
Lower function	no	yes	yes
Bulk	small	medium	large

Petzl revealed Maestro in 2017, but for some reasons, Maestro delayed for two years, finally launched

in 2019. If you check it carefully, you could find the positions of two axis are different.

                                           Maestro 2017 sample

                                                 Maestro Product

ASAT from China also introduced their pulley type self-locking descender RD1 in 2017. It’s more

like a engineering prototype at that time. After 4 years optimization, it has been evolved into RD2.

CMC introduced Clutch in 2019. Compared with MPD, Clutch is a ID-like device, much more ergonomical.

Many users are curious about the efficiency of pulley.Actually, there’re many factors will affect the

efficiency of the pulley. And there’s no test procedure and requirement about efficiency on EN 12278.

 Different test configurations, experimental errors and data processing method will also bring different

results. Petzl has a good introduction about efficiency, but it just concerns their own products.

Link below:

https://www.petzl.com/INT/en/Professional/Pulley-system-efficiency-tests-with-MAESTRO--I-D-S--PRO-TRAXION--ROLLCLIP--SPIN-L1--SPIN-L1D---?ProductName=MAESTRO-S

So I think the efficiency data is only fair to compare when the devices tested under the same condition.

After collected all the descenders we need, my friend Lee and I did an efficiency test in the same test

configuration.

Load cell : enforcer ( slow mode).

Rope: Edelrid Static Low Stretch 10.5mm (new);

Lifting power by a 500kg manual winch.

 

Result:
  

		RD2	CLUTCH S	MPD S	Maestro S
1:1 （100kg）	Average   pulling force	109kgf	133kgf	109kgf	115kgf
	Efficiency	91%	75% （71%  official 11mm）	91%  （88% official 11mm）	86.9% （86% official 10.5mm）
3:1 (133kg)	Average pulling force	48kgf	50kgf	53kgf	48kgf
	Actual mechanical ratio	2.77: 1	2.66 :1	2.51：1	2.77：1 （2.5：1 official 11mm）

 

		IDS	LOV3	GIANT	RIG	ATC   GUIDE
1:1 （100kg）	Average pulling force	288kgf	190kgf	223kgf	273kgf	/   *
	Efficiency	35% （31% official 11mm）	52%	45%	37%	/
1:3 (133kg)	Average pulling force	62kgf	/	60kgf	/	64kgf
	Actual mechanical ratio	2.14：1	/	2.21：1	/	2.08：1

		SIMPLE	SPARROW	Petzl   OK carabiner	Petzl   SPIN pulley	Petzl   SPIN pulley 125kg	ROCK EXOTICA 1.1’pulley  125kg
1:1 （100kg）	Average pulling force	319kgf	205kgf	192kgf	106kgf	133kgf	131kgf
	Efficiency	31%	48%	52%	94%  (88%   official 11mm)	94%	95%

 *Note：Due to time limit, we don’t test all the descenders.

    
    
    

Conclusion:  
1:1 test explains basic and reference efficiency. In practical, we seldom directly raise a victim via a descender.

However, according to this basic efficiency, we could figure out how does the construction of the device affect

the efficiency. 

When it comes to 3:1 mechanical advantage system, the built-in 2:1 pulley system plays a big role in pulling.

This leads to the slight differences in the basic efficiency of descenders is not that important. And the becket

hole allows more complex rigging for a more efficient mechanical advantage system.

(The only question in the tests is the efficiency of 3:1 MPD is lower than Clutch, maybe due to some errors,

I’ll do it again further.)

Efficiency is only one aspect, the performance of the descenders includes a lot… and also includes your personal

review.

MPD is a substitute of old RPM 3:1 system by CMC . It’s a typical anchor use descender. I think it’s an

over-engineered device, ignored the ergonomic design. Depends on the unique features, MPD dominated

the market for almost ten years.

 Maestro is definitely a strong competitor to MPD, and there’s the Large version for the US market. Very similar

working principle to MPD. It’s also a device designed for anchor use. Plus, a cheaper price.

The only thing I dislike is the side plate can’t be opened when the device is connected. And the attachment hole

is too thick to connect an Oval carabiner. Several times, I almost failed to catch it on heights.

There’re many differences between Clutch and others. Very unique and clever working mechanical design.

Much more ergonomical. The operation method is very similar to the classical descender and it’s much more

like a personal descender in the series of CMC. CMC has continued MPD production can also prove this.

Clutch has the anti-panic function, it’s good for personal descending use. However, not friendly used on anchor

lowering on low angle slope. The anti-panic usually engages with only one person load.  

Strictly speaking, the prototype of RD2 is the second pulley type self-locking descender in the world.

After years improvement, RD2 has had a large market share in Chinese market. But it’s still a little-known

company in worldwide rope access community.

 RD2 seems like an ergonomical version of MPD for personal use. It passed EN 12841C-150kg test. Lightest

compared with others. You could also use it on anchor.

I think the only drawback on RD2 is the axis of side moving plate is same to MPD, It can’t be fully opened,

not friendly to rope installation.

Here is the specifications

	MPD S	Maestro S	Clutch S	RD2
Rope diameter	11mm	10.5-11mm	10.5-11mm	11mm
Anti-panic	no	no	yes	no
Weight	1200g	1100g	836g	790g
Maximum working load	272kg	250kg	272kg	200kg
Personal descender	no	no	yes	yes
Anchor descender	yes	yes	yes	yes
Certifications	EN12841C EN341  EN 12278 NFPA  ANSI	EN12841C EN341  NFPA	EN12841C EN341  NFPA ANSI	EN12841C