Abstract:
A firefighting nozzle comprises an elongated barrel having a inlet opening at one end for engaging a source of fluid under pressure and a discharge opening at an opposite end for engaging a discharge element for dispensing the fluid under pressure. A valve arrangement includes a slide valve element slidably mounted within the barrel for reciprocating movement along the length of the barrel to adjust the flow of fluid through the barrel. The nozzle includes a pistol grip trigger assembly mounted on the barrel that includes a segment gear pivotably for engaging a toothed surface of the slide valve element so that rotation of the segment gear causes reciprocation of the slide valve element. A four-bar linkage arrangement is incorporated between a manually actuated trigger to translate depressing the trigger to controllable reciprocation of the slide valve element. The four-bar linkage provides a mechanical advantage that allows the firefighter to easily control the trigger and thus the fluid discharge from the nozzle.

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a non-provisional utility application claiming priority to provisional application No. 62/155,061, filed on Apr. 30, 2015, the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     This disclosure relates to handheld nozzles connected to a fire hose. Firefighters often use this type of nozzle to extinguish fires in situations such as homes, cars, flammable liquid spills, and commercial properties where critical flow rates of at least 95 GPM (360 L/min) and pump pressures of at least 100 PSI (7 bar) are needed to overcome the fire. These nozzles develop reaction force of at least 50 lbf (23 kg) as a result of accelerating the water to velocities need for projecting fluids such as water acceptable distances and to form droplets into effective sizes. It&#39;s not uncommon for the reaction force to exceed half the weight of a firefighter. The physical limits of firefighters are oftentimes stretched to their maximum in the few moments a heavily laden firefighter with air pack rushes up many flights of stairs to rescue victims, setup firefighting equipment, and battle the blaze in incredibly hot rooms with near zero visibility conditions. 
     Added to that are forces from typical 1¾″ (45 mm) diameter hose filled with water, and the associated stiffness which increase the effort of restraining the nozzle to direct the trajectory in the desired direction. One hand has traditionally been dedicated towards this task, while a second hand is used to open and close the valve feeding water to the nozzle, leaving no hands free to help stabilize the fireman, drag hose, or tend to a hundred other tasks which might prove beneficial. 
     Dedicating a second hand to operating a valve handle has been the expectation given that the force to move lever operated valve handles is fairly high owing to the large frictions and forces resulting from high fluid pressure. For example National Fire Protection Association standard NFPA 1963, 2013 edition requires valve lever operating forces between 3 lbf (13.4 N) to 16 lbf (71.2 N) per section 4.6.3. Prior to institution of this standard it was not uncommon for valve handle levers to operate with at least 40 pounds pull. 
     Trigger operated nozzles are those whose valve is operated by a gripping force of the fingers. It&#39;s not uncommon to see nozzles of this type used for purposes such as use from a garden hose, for agricultural irrigation, chemical spraying (including pesticides and herbicides), paint spraying, or wash-down. This type of valve allows one to use a single hand to hold and operate the nozzle, and allows the flow to quickly turn on, and for the valve to shut off quickly by itself. 
     Triggers are not used to move a traditional valve on a firefighting nozzle. Lever handles on firefighting nozzles generally move along an arc distance of about 8 inches (20 cm) while a comfortable finger grip motion distance for a trigger is not even a fourth of that. Therefore an ordinary firefighting valve simply fitted with a trigger instead of a lever would have at least four times higher operating force. Finger muscles on this trigger would therefore be required to produce over four times as much force as the more powerful arm and shoulder muscles moving a lever. Inherently, this approach sounds unworkable. 
     Trigger operated nozzles are commonplace in small firefighting hoses at far lower flows, which is to say 1″ diameter hose (25 mm) and flows 60 GPM (240 L/min) or less. Trigger valves of a wide variety lend themselves to these conditions because a person&#39;s strength far exceeds operational forces encountered making trigger valves acceptable from an ergonomics standpoint. 
     Trigger valves lend themselves to the rapid valve on/off pulsing techniques found to be beneficial in controlling the atmosphere of rooms filled with un-ignited highly flammable superheated combustion byproducts, but up until now these nozzles were produced with maximum flows generally considered to be too small for safe structural (residential and commercial) firefighting. This technique is sometimes referred to flashover pulsing. 
     However, up until now larger sized trigger valves have not been commercialized for firefighting (larger, as described in the opening paragraphs) because of various obstacles to scaling up their size which made their use unacceptable, including reasons such as;
         Fingers don&#39;t produce enough force to comfortably open a substantially larger valve element because fluid pressure acting on larger areas results in larger forces.   Frictional forces and seal drag caused by preload and fluid pressure to move larger valve elements make it difficult for fingers to operate the trigger.   Once opened, significant closing forces are often generated by fluid pressure and dynamic velocity in valve types used on small trigger nozzles. These forces while insignificant in smaller valves can become untenable if scaled up to larger valve sizes making it difficult for fingers to retain the valve in an open position.   Engaging a locking device to retain a valve in a flowing position generally cancels the safety benefits of a self-closing valve in the event of loss of grip on the nozzle. An unrestrained garden hose nozzle carries little risk of injury, whereas a 1¾″ hose whipping at 50 MPH can kill nearby people.   Trigger valves typically shutoff in an instant which is OK for small trigger nozzles, but becomes detrimental with larger sizes as nearly instantaneous deceleration of a large water mass produces significant water hammer which carries risks such as injury from catastrophic hose rupture, loss of extinguishing or protective flow, and the physical stress of sudden impulse change.   Physical size and weight of the nozzle would become unacceptably large if smaller trigger valves were simply scaled up.   Scaling up a small valve scales up the stroke needed to achieve a reasonable flow which also scales up the distance required operate a trigger to where it becomes larger than the grip capacity of a typical person&#39;s fingers.   Trigger valves generally are arranged so that the liquid enters the nozzle from the bottom and undergoes a direction change as it passes thru the front of the nozzle, thus the nozzle trajectory is neither parallel nor co-linear with the hose feeding it. As a result the hose is not positioned to absorb significant portions of the nozzle reaction force.       

     Prior nozzles employing hydraulic control circuits such as disclosed in U.S. Pat. No. 5,261,494 to McLoughlin et. al. (the disclosure of which is incorporated herein by reference) move sliding valve elements between open and closed positions using chambers of water opened and closed by trigger position. However these valves have no positive mechanical engagement between trigger and sliding element so the position of the sliding element with respect to the trigger is subject to some uncertainty. For example; one could expect the valve to be fully closed at the start of a fire based on trigger position, only to find the valve element stuck open from lack of lubrication, corrosion, or from water supplies to the hose being terminated with the trigger depressed. Furthermore, water in hydraulic control circuits is subject to freezing in cold temperatures thus disabling the valve sooner than freezing occur in the full diameter of the waterway of a mechanically operated valve. Although springs added to the moving element could improve uncertainty somewhat, prudent safety practices would discourage use of hydraulically controlled trigger valves. 
     All of the prior firefighting nozzles will exhibit at least one of the drawbacks described above if scaled up. Moreover, all of the commercially available trigger operated firefighting nozzles have the water enter the bottom of the nozzle, at a significant angle to the discharge line of action. 
     Lever handle slide valves have found widespread use in the field because of the ease of which the handle may be operated, and the relative lack of turbulence. Attempts to move slide valves of this type by a straight linear pull, or by using a simple lever with a pivot point have resulted in valves with substantial risk of water hammer, and relatively high forces on the slider making them difficult to open with finder pull, and susceptible to self-opening or closing tendencies at various flows and pressures. A new mechanism therefore is needed. 
     SUMMARY OF THE DISCLOSURE 
     The present invention contemplates a trigger valve for a firefighting nozzle with flow rates of at least 95 GPM (360 L/min) and pump pressures of at least 100 PSI (7 bar) which has a combination of at least two or more of the following attributes:
         A trigger operated slide valve that can be restrained, opened, and closed with only one hand;   A valve with opening forces low enough to permit the fingers to comfortably open a substantially larger valve element against forces generated by fluid pressure acting on a slider with a substantially large waterway;   A valve whose frictional forces and seal drag are modest enough for the fingers to comfortably move a slider with a substantially large waterway against forces caused by preload and fluid pressure;   A valve that once opened, has modest closing forces, making it easy for fingers to retain the valve in an open position;   A locking device to retain a valve in a flowing position which self-disengages to yield “dead man control” safety benefits of a self-closing valve in the event of loss of grip on the nozzle. An unrestrained nozzle under high flow tends to whip violently resulting in risk of death by blunt force trauma;   A valve whose closing speed is infinitely adjustable to a variety of speeds where in one extreme condition it will shut off almost instantaneously, and in another extreme shuts off over several seconds, thereby allowing the firefighter the ability to optimize the best balance between water hammer and closure in a timely manner. A nearly instantaneous deceleration of a large water mass produces significant water hammer which carries risks such as injury from catastrophic hose rupture, loss of firefighting ability, and the physical stress of sudden impulse change, whereas closure in too long of a time results in risk of hose whipping in the event of loss of grip on the nozzle;   A nozzle whose physical size and weight is acceptable when compared to nozzles of similar flow capability;   A valve whose trigger has a stroke of a length comfortable to the grip capacity of a typical person&#39;s fingers;   A trigger valve arranged so that the liquid enters the nozzle from the back, and passes flow to the front of the nozzle resulting with a nozzle discharge trajectory that is nearly parallel or co-linear with the hose feeding it which results in several benefits including;
           The hose is positioned to absorb significant portions of the nozzle reaction force while a firefighter is in the standing position. Standing positions are ideal for exterior fire attacks such as wild-land fires, but are dangerous during interior fire attacks because thick smoke, gasified explosive fuel, and heat all accumulate at the ceiling. Therefore firefighters position themselves on the floor in a crawling, kneeling, or lying stance while operating inside buildings during interior structural fire attacks;   When firefighters are positioned on the floor, fire hose is easier to drag when the hose is laid parallel to the direction of travel towards the fire, especially when advancing down a long narrow hallway;   When firefighters are positioned on the floor, there is equal freedom to swing the nozzle from side to side, or up and down without having to fight the angle of the hose inlet;   When firefighters are positioned on the floor, firefighters know that hose is being advanced into a “cool zone” which they formerly occupied rather than being forced to arch to the left or right by the angle of the hose inlet which could potentially place the hose in hot embers, down stairways, or down through holes burnt in the structure. As a result there is less risk of water depravation by hose burning thru. Since visibility is oftentimes nonexistent, firefighters must follow the hose by feel into or out of the fire. It could be life threatening to mistakenly follow a hose into a hole or down stairs;   
           A pistol grip with trigger which can be built as a self-contained replaceable subassembly which can be attached onto a variety of valves;   A pistol grip with trigger subassembly which can be built with differing lengths of stroke appropriate to either flow larger volumes of water at lower pressures by using a longer stroke with lesser mechanical advantage, or to flow smaller volumes of water at higher pressures by using a shorter stroke with greater mechanical advantage. As a result finger pull is not compromised in either condition;   A valve body with an outlet connection which can accept a variety of nozzle front ends, including those permanently installed as well as a hose threaded discharge;   A pistol grip whose grip surface is easily replaced in the event of excessive wear from dragging over pavement, being dropped, or being driven over;   A pistol grip whose grip surface is easily interchangeable with those produced in other colors;   A trigger valve that is mechanically connected to push and pull a slider between its open and closed positions.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified perspective view showing a trigger slide valve in use 
         FIG. 2A  thru  2 D are external isometric views showing four nozzle configurations. 
         FIG. 3  is an exploded view on one of the nozzle configurations shown in  FIG. 1 . 
         FIG. 4  is an external partial exploded view showing interchangeability of various trigger assemblies on a valve. 
         FIG. 5  is an exploded view of the trigger assemblies of  FIG. 3  depicting components with variations in stroke lengths. 
         FIGS. 6A, 6B, and 6C  are cross section views of  FIG. 2  depicting adjustment positions of a dampening mechanism in its least dampened mode, partially dampened mode, and most dampened mode respectively. 
         FIG. 6D  is a cross section view of a modified dampening mechanism in is most dampened mode. 
         FIGS. 7A, 7B, and 7C  are cross sectional view of  FIG. 2  depicting the valve in the fully closed, partially open, and fully open positions respectively. 
         FIG. 8  is a graph of axial load on slider versus slider position. 
         FIG. 9  is a graph of axial forces due to water pressure at various slider positions. 
         FIG. 10  is a graph which characterizes mechanical advantage. 
         FIGS. 11A and 11B  depict diameters influential to the axial forces of water on the slider. 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles disclosed herein as would normally occur to one skilled in the art to which this disclosure pertains. 
     In all of the drawings, the direction of flow is depicted as moving from left to the right.  FIG. 1  shows a typical layout of a firefighter extinguishing a blaze using a trigger operated slide valve nozzle V. Water from a source such as a hydrant S is delivered by a supply hose H to a fire pump T which increases the pressure. Flow from the pump is delivered to the valve nozzle V using a fire hose F. The firefighter grasps the nozzle, operates the valve V, and directs water along a trajectory to extinguish the blaze, while restraining various forces. The nozzle depicted in  FIG. 1  includes a trigger operated slide valve which is shown being operated by a firefighter using his first hand which is being used to restrain the nozzle as well as squeeze the trigger, while the second hand is being used to signal another firefighter. The second hand can also be used for many tasks such as gripping onto a vehicle to stabilize oneself while spraying liquid from a moving vehicle, to drag or reposition hose while changing positions within a burning structure, or to operate doors. 
       FIGS. 2A, 2B, 2C, and 2D  depict four types of nozzle with a trigger operated slide valve. Each nozzle includes a shutoff valve and grip assembly extending below it operated by a trigger. Each grip assembly is securely mounted to a slide valve. Each slide valve has an inlet coupling on its inlet end to which a fire hose can be connected, and a nozzle front end on its outlet end from which water is discharged to the fire. 
     It can be seen that the same type of grip assembly can be used on many types of nozzles to meet the needs of Fire departments who have grown accustomed to choosing a variety of different nozzle types. For example two different sized valves are depicted allowing nozzles to be optimized to deliver larger flows as shown in  FIGS. 2B and 2C , or with smaller flows as shown in  FIGS. 2A and 2D . 
     Valve inlets are ideally designed for interchangeable installation to a family of inlet couplings allowing connection to fire hoses of various waterway diameters and hose connection types found around the world. For example 1″ (25 mm) hose threaded couplings used in USA are depicted in  FIGS. 2A and 2D , while a 2″ (52 mm) Storz quick connector well known in Germany is depicted in  FIG. 2B , and a 1.5″ (38 mm) threaded coupling common to North America is shown in  FIG. 2C . 
     Furthermore, the front ends of the nozzle may include fixed orifice basic spray nozzles with a spray shape adjustable between straight stream and wide fog as shown in  FIG. 2B , as well as more advanced nozzle designs allowing manual control of orifice size as shown in  FIG. 2A . The nozzle front ends may also include a pressure controlling mechanism responsive to maintain velocity as shown in  FIGS. 2C and 2D , or may be adapted to produce a firefighting foam from a solution of water mixed with foam using a foam aspirator, one type of which is depicted in  FIG. 2B . Therefore, valve outlets constructed with a common connection to fit many nozzle front ends are preferred. 
       FIGS. 3 and 5  are partial exploded views of a trigger assembly  100  showing the components which drive the valve along its travel path to open and close the valve. The assembly is built on a main structural element called a pistol grip  690  which includes cross holes  691  forming a trigger pivot axis into which ride a screw, a lobed shaft  205 , the trigger  204 , a lever arm  203 , and a retainer nut  104 . A pair of spacers  105  and  105 ′ space the components to prevent rubbing. The lever terminates in a tip hole  203   a  within the tip of the arm. Various lever arms  203  may be made with different lengths between the pivot axis  691  and the tip hole  203   a , enabling arms of various lengths to be interchangeable on the valve, including a short length lever and a long length lever. Rotational motion of fingers gripping the trigger  204  is transmitted to the lobed shaft  205  by the conjugate lobed shape of the shaft opening  204   a  fitted there between. Rotation of the lobed shaft  205  is then transmitted to the lever arm  203  by the conjugate lobed shape of the opening  203   b  in the lever arm. 
     The lever arm  203  is connected to a segment gear  200  by a link  201 , with one end of the link attached to the lever arm with a pin  625 , and the opposite end of the link attached to the segment gear by a pin  626 , each pin press fit into a corresponding bore in the lever arm and segment gear. The gear  200  has teeth  200   a  protruding from its upper portion which are arranged to be concentric about a pivot hole  200   b  defined in the gear. A gear pivot pin  187  engages a pivot hole  692  in the grip  690  and the pivot hole  200   b  in the gear  200  and can be retained with a set screw  188  along the gear&#39;s pivot axis. The gear teeth  200   a  engage mating teeth  301   a  on a valve element  301  disposed within a nozzle  300 , as shown in  FIGS. 7A-7C . 
       FIG. 4  shows trigger assemblies  100 ,  100 ′ of  FIG. 3  having different sized lever arms  203 ,  203 ′ arranged for easy connection a nozzle assembly  300  in a manner similar to the nozzles shown in  FIGS. 2A-2D . The maximum opening of the valve can be reduced to a lesser size by using a trigger grip assembly configured with a shorter stroke which is beneficial when operating on a high pressure pump so as to prevent excessive fluid from being discharged, and to increase the mechanical advantage of the trigger enabling it to overcome higher pressure without excessive grip force. Thus, the lever arm  203  has a greater distance between the pivot point  103  to the pivot connection  625  with the link  201 , than for the lever arm  203 ′. The trigger assemblies  100 ,  100 ′ are configured to be readily interchangeable for attachment to the nozzle  300 . Thus, the grip assembly may be connected to the nozzle using fasteners such as screws. 
       FIG. 5  is an enlarged exploded view of the trigger assembly of  FIG. 4  depicting linkage components or lever arms  203 ,  203 ′ with different stroke lengths. Squeezing the trigger moves the lobed shaft  205  to rotate, which thus causes the lever arm  203  to rotate with the lobed shaft. Rotation of the lever arm causes the link  201  to pivot and translate, which then causes counterclockwise rotation of the gear segment  200 . The teeth  200   a  of the gear segment engage the teeth  301   a  to move the valve element  301  between a closed position, as shown in  FIG. 7A , and various open positions, as shown in  FIGS. 7B-7C . The lever arm, link and gear segment thus act as a four-bar linkage to convert motion of the trigger as it is squeezed into translation of the valve element  301  to adjust the fluid flow through the nozzle assembly  300 . 
     The four-bar linkage is constructed so that the link  201  is at an angle α relative to a line between the pivot point  103  for the lever arm  203  and the pivot point  626  between the link and the gear segment  200 , as illustrated in  FIG. 6C . As seen by comparing the position of the four-bar linkage among  FIGS. 7A-7C , the angle α can be in the range of 40-60° in the closed position of  FIG. 7A , to an angle α in the range of 0-20° in the fully open of  FIG. 7C . In the fully open position of  FIG. 7C , the axis of the link  201  is preferably as closely aligned with the line between pivot points  103 - 626  as possible without being exactly co-linear. A small angle α can dramatically increase the mechanical advantage provided by the four-bar linkage to allow the firefighter to easily hold the trigger in this full open position even under the extreme pressure exerted by the fluid flow through the nozzle. However, an angle α of exactly zero can limit or even inhibit the ability of the nozzle to rapidly return to a lower flow position when the trigger is released. In a specific embodiment the angle α is less than 10° in the full open position. 
       FIGS. 6A, 6B, and 6C  are cross section views depicting a damping mechanism  400  associated with the trigger nozzle and the four-bar linkage used to control the valve component  301  ( FIG. 7A ). The damping mechanism  400  is shown adjusted between a minimum dampened mode ( FIG. 6A ), a partially dampened mode ( FIG. 6B ), and a maximum dampened mode ( FIG. 6C ). The dampening mechanism includes a dampening fluid  700 , whose viscosity remains nearly constant over a wide range of temperatures. One preferred fluid is Dow Corning synthetic silicone dampening fluid. Rotation of the segment gear  200  causes axial motion of piston  701  because of engagement of pin  702  between piston push hole  701   a  and a pair of fork slots  200   c  ( FIG. 5 ) on the end of the gear  200  opposite its teeth  200   a . The slots  200   c  are long enough to maintain contact between the segment gear  200  and the pin  702  throughout the range of rotation of the gear as shown in  FIGS. 7A-7C . 
     Axial motion of the piston is guided on the end nearest the piston push hole  701   a  by a guide  705 , and on its opposite end  701   b  by a guide bore  694  within the pistol grip  690 . The guide bore  694  also serves to locate the guide  705  coaxially with the guide bore and piston. Also fitted within the guide bore is a lower cap  703  which is threadedly engaged within the pistol grip  690 . The lower cap  703  defines a cap guide bore  703   a  and internal threaded section  703   b  into which is screwed a speed adjuster  710 . Dampening fluid  700  is retained in a dampening fluid zone  700   a  by appropriately-sized O-ring seals  712  at four locations; on the interior and exterior of the guide  705 , on the exterior of the cap  703  and on the exterior of the adjuster  710 . 
     Also disposed in the dampening fluid zone is a compression spring  715  which is positioned to urge the piston  701  toward the lower cap  703  to bias the valve to its closed position. A cup seal  755  is disposed in a groove  756  defined in the circumference of the larger end  701   b  of the piston and is engaged to slide within the guide bore  694 . The piston includes an axial fluid passage hole  760  and a traverse fluid passage hole  765  ( FIG. 6C ). 
     The dampening fluid zone  700   a  is divided into two chambers  700   b  and  700   c  ( FIG. 6C ). A spring fluid zone chamber  700   b  is defined as the region surrounding the spring  715 , bounded by the guide bore  694 , the guide  705 , and the portions of the piston proximate the spring. An adjuster fluid zone chamber  700   c  includes the region bounded by the adjuster  710 , the end of the lower cap  703  nearest the piston, and the large end  701   b  of the piston.  FIGS. 6B-C  show the relationship of the trigger grip assembly while the valve is in a closed position which corresponds to minimum fluid volume of the adjuster zone chamber  700   c , and maximum fluid volume of the spring chamber  700   b.    
     As the nozzle&#39;s valve is opened to discharge water to the fire, dampening fluid can move between the chambers by either forcing it through the fluid passage holes  760 ,  765  past the small end of the adjuster  710 , or past the cup seal  755  which can only restrain significant dampening fluid pressure in one direction owing to the direction in which it is installed. The cross section of the cup seal is V-shaped and is installed with the opening of the V nearest the cap  703 , while the vertex of the V is nearest the guide  705 . In this way the cup seal  755  not only acts as a check valve, but also adds negligible friction to the opening stroke. 
     As the nozzle&#39;s valve is closed, the cup seal  755  is energized by fluid pressure, so motion of the piston  701  towards the cap  703  must empty fluid out of the adjuster chamber  700   c  by flowing back into the spring chamber  700   b  thru the fluid passage holes  760 ,  765 . 
     If the tip of the adjuster is adjusted along its length to the adjuster position shown in  FIG. 6A  then fluid is free to pass between chambers in both directions without restriction of the adjuster, thus the valve will close at maximum speed—i.e., with minimal dampening. If the adjuster is threaded inwards to the position depicted in  FIG. 6C  then fluid must pass between a small gap defined by the annulus existing between the internal diameter of the axial fluid passageway  760  and the outside diameter of the adjuster tip  710   a . In this adjustment position, the entire closing stroke has been dampened, and the valve will close slower over its entire stroke from full-open to full-closed. If the adjuster is set to some midway position then dampening over a portion of the stroke may be obtained by selecting the desired adjuster position. The position depicted in  FIG. 6B  shows the adjuster tip  710   a  just entering the axial fluid passageway  760  as the valve  301  comes to its fully closed position ( FIG. 7A ). 
     Dampening is desirable from two standpoints—it reduces the water hammer in the hose caused by decelerating the mass of water in the fire hose, and it reduces the rate of change of nozzle reaction caused by the nozzle&#39;s acceleration of water discharged toward the fire. Abrupt changes in flow can cause the fire hose F to “jump” a few inches as the hose becomes stiffened and lengthened by pressure increase and from transient shock waves caused by water hammer. The combination of these two effects on the firefighter&#39;s hands, arms, back, and joints, can be loosely equated to the effect of being kicked by a kick boxer. 
     More dampening is generally desirable to lessen water hammer in the hose when using fire hoses capable of higher flows because the mass of water times it&#39;s velocity in the hose has a larger kinetic energy than with smaller flows. More dampening is also desirable as pump pressures become higher because higher pressures tend to increase flow as well as nozzle pressure, thereby increasing nozzle reaction force. More dampening may be needed when operating temperatures are higher to compensate for the viscosity reduction of the dampening fluid, or to compensate for poor footing in slippery conditions. 
     On the other hand, too much dampening inhibits the desire to rapidly pulse the water on and off for flashover pulsing. Too much dampening can also decrease safety by increasing the length of time an unrestrained nozzle can flow before shutting itself off thus coming to rest. The adjuster  710  which can be adjusted to dampen only the desired portion of the stroke enables ergonomic selection of the most suitable dampening. It is contemplated that the volume  700   a  may include some air to compensate for volumetric variations due to temperature fluctuations. 
     A modified dampening mechanism  400 ′ is shown in  FIG. 6D  that is similar in construction to the dampening mechanism  400  but with some modifications to the piston  701 ′ and the speed adjuster  710 ′. In particular, the opposite end  701   b ′ of the piston  701 ′ is provided with a large dampening fluid zone bore  700   a ′, as shown in  FIG. 6D . The adjustment tip  710   a ′ of the speed adjuster  710 ′ extends into the bore  700   a ′ to control dampening fluid flow through the bore. The adjuster tip  710   a ′ defines a central bore  720  that communicates with a side outlet  722  by way of a narrow cross bore  721 . As shown in the detail view in  FIG. 6D , the outer diameter of the adjuster tip  710   a ′ is sized to leave a flow gap  723  between the tip and the piston end  701   b ′ so that a small amount of dampening fluid is always in communication between the dampening fluid zone  700   a ′ and the main bore  700 . The size of the cross bore  721  controls the rate of flow of this collateral dampening fluid to thereby provide incremental velocity control of the dampening mechanism  400 ′. Different speed adjusters  710 ′ may be provided with different cross bore diameters to achieve specific velocity profiles. 
       FIGS. 7A, 7B and 7C  are cross section views of the nozzle of  FIG. 2C  depicting the valve in the fully closed, partially open, and fully open positions, respectively. Referring now to  FIG. 7A , water from the fire hose enters the nozzle  300  through inlet opening  300   a , and a coupling  300   c  adapted to couple to a source of fluid, such as a fire hose. The water flows through the valve body and slider  301  to the outlet opening  300   b . As depicted in  FIG. 7A , the inlet opening  300   a  and the outlet opening  300   c  each define a corresponding flow axis A 1 , A 2 . In one aspect of the present disclosure, the two flow axes A 1 , A 2  are substantially parallel and in one specific embodiment are substantially collinear. This is in contrast to the conventional firefighting trigger nozzles in which the water inlet is transverse to the water outlet. 
     The trigger assembly  100  is mounted to barrel of the nozzle  300  at a non-parallel and non-collinear orientation relative to the flow axes A 1 , A 2 . In particular, the trigger assembly is mounted so that the pistol grip  690  projects downward from the barrel, as shown in  FIG. 7A . This allows the firefighter to grasp the trigger assembly in a comfortable and ergonomically effective orientation. 
     The slider  301  in the closed position abuts axially against a valve plug  302  which forms a sealing surface against the slider at the point of contact. The interior surface of the slider is entirely wetted with water, whereas the exterior surface of the slider is fitted within the valve body  302  to move axially along engagement with a mating valve bore  303 . A pair of slider O-ring seals  304  of equal diameter seal water from leakage around the exterior of the slider. Additional seals at the inlet coupling, hose connection, and at the connection between the valve body and the nozzle&#39;s front end maintain liquid within its flow path. 
     Considering the motion of the slider by itself (i.e., without the effect of the trigger grip assembly), if the diameter of the point of contact of the slider  301  with the valve plug  302  is identical to the diameter of the slider O-ring  304  nearest the coupling, then fluid pressure does not impart axial force on the slider because the net area in the axial direction is zero. Therefore even under high pressure the slider can be moved towards its open position by merely overcoming slider seal friction. 
     Axial motion of the slider  301  is imparted by the trigger grip assembly  100  by engagement between the segment gear teeth  200   a  and conjugate rack teeth  301   a  formed into the outside of the slider  301 . The valve will open if the trigger  204  is squeezed creating a conical valve opening annulus  306  ( FIG. 7B ) between the slider  301  and the valve plug  302  at what had been their sealing point. Fluid from the opening continues into the front end of the nozzle  300  until a point at which its velocity is increased by the discharge orifice  310  which is the minimum flow area. The orifice of  FIG. 7B  occurs as water pressure acts against a spring mechanism  312 . Water discharged past the orifice may be shaped into a straight jet by a shaper  314  as shown, or may be discharged as a conical spray of various angles as the shaper is partially or fully retracted according to common practice. 
     The trigger  204  may be depressed further to open the valve fully to the position depicted in  FIG. 7C  which moves the slider  301  further towards the coupling and away from the valve plug  302 , thus creating a larger conical valve opening annulus  306 ′, and the maximum flow. Dynamic forces of water flowing through the slider produce an axial force tending to close the valve as a result of frictional drag through the slider. The piston spring  715  of the damper assembly  400  also creates a force increasing the valve&#39;s tendency to close. These forces are larger than can be resisted by finger squeeze alone, thus the relative position and orientation of the 4-bar linkage in this position are used to overcome the forces as the link  201  and the arm  203  come into near alignment, as shown in  FIG. 7C , forming a nearly self-locking four-bar linkage. In this way, near zero force is needed to retain the valve in the fully open position. 
     At times it is desirable to hold the valve  300  at a set position for an extended length of time. Therefore a lock lever  250  is positioned on the trigger  204  on a lock lever pivot  252 , as shown in  FIGS. 5 and 6A . The lock lever  250  includes a detent  254  that can be urged into locking engagement with serrations  305  on the pistol grip  690  by merely pressing a finger against the lock as the valve is opened, and then releasing the trigger to retain a locked position. Thus, as shown in  FIGS. 7B-7C , the lock lever  250  can be locked at different positions relative to the pistol grip, with the positions corresponding to configurations of the 4-bar linkage, and ultimately positions at which the valve  301  is locked. It can be appreciated that partially squeezing the trigger or even dropping the nozzle is enough to release the lock lever  250  from engagement with a serration  305  due to urging of a lock compression spring  308  that bears against a surface  308   a  of the trigger  204 . As seen in  FIG. 6A , the spring  308  is oriented relative to the pivot  252  to provide a force that pushes the detent  254  up and away from the serrations  305 . 
       FIG. 8  is a graph showing the axial forces acting on a slider of a lever operated slide valve nozzle commercially sold by task Force Tips, Inc., under the trademark G-Force™. This valve size is identical to that of the large trigger valve size depicted in  FIGS. 2B and 2C . The G-Force™ lever type valve has detents on the lever to retain the slider at various set positions under the axial forces of water flow and pressure. The slider of this type has a substantial positive net area difference between the O-ring seals, and the slider&#39;s point of contact resulting in a positive axial load force towards the closed position, and near zero axial force at the maximum slider position, which corresponds to the valve&#39;s opening. A slider position of zero is the closed position, while moving it fully results in nearly a half inch of travel. An opening force of over 100 pounds is needed to move the slider, so it can be seen that using grip force alone without mechanical advantage is unlikely to result in a trigger valve which is easy to use. On the other hand, the force needed to close the valve once fully opened is less than zero, indicating a trigger valve which would remain stuck in the open position. 
       FIG. 9  is the corresponding graph for a trigger operated slide valve according to the present disclosure. The forces acting on the slider are substantially less owing to the substantially less positive active area on the slider. The valve plug is preferentially made from ultra-high molecular weight polyethylene which has good abrasion resistant and sealing abilities. As flow commences the slider moves back slightly and the force on the slider increases as a result of fluid velocity increasing along the face of the slider in regions formerly in sealing contact with the valve plug according to the Bernoulli effect which is to say pressure (thus force) decreases where velocity increases. Hydrodynamic force on the slider in the full open position is near zero in the fully open position. 
       FIG. 10  depicts the kinematics of a trigger valve linkage mechanism according to the present disclosure. The curve labeled “Motion” denotes how input motion from squeezing the trigger will produce a clockwise rotation of about 35 degrees, resulting in a counterclockwise rotational output to the segment gear of about 30 degrees. The other curve denotes how mechanical advantage of the trigger (times ten) increases radically as the trigger moves the valve towards it&#39;s fully opened position. The 4-bar linkage of the present disclosure gives the firefighter&#39;s fingers more mechanical advantage to retain a fully opened slider position against the higher forces of the fully compressed spring and the hydrodynamic force at maximum fluid velocity tending to drag the valve closed, without being so near a self-locking four-bar linkage position as to risk the linkage becoming stuck in the full on position. Self-locking occurs when the pivot pin joining the arm to the link is in alignment with both the trigger pivot axis and the pivot pin joining the link to the segment gear, as angle α is equal to or less than zero ( FIG. 6 ). 
       FIGS. 11A and 11B  show the preferred diameters and active areas of a trigger operated slide valve rated for flows up to 200 GPM (760 L/min). Water pressure causes an axial force on the slider in the closed position because O-ring sealing diameter D 1  is larger than valve seat contact diameter D 2 . This surface projected area on the preferred slider is about 0.074 square inches, which causes about 15 pounds force (6 kg) at 200 PSI (14 bar) in the closing direction of the nozzle. The preferred spring force from the trigger grip assembly contributes an additional 3 pounds axial force (1.4 kg) to the slider in the closing direction. 
     In the partially open position shown in  FIG. 11B , high velocity water passes across the end of the slider, thus axial force of water on the slider tend to be dominated by the difference in area between diameters D 1  and D 3 , and frictional drag along the inside of the slider&#39;s waterway. 
     By ratio and proportion it is believed that the fire-fighting nozzle and valve of the present invention can be scaled up to include larger valves capable of flows in the range considered manageable for firefighting with hand-held nozzles, without exceeding reasonable limitations of finger squeeze. 
     The present disclosure should be considered as illustrative and not restrictive in character. It is understood that only certain embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.